Security fixes, enterprise stuff and more (#3241)

# Description of Changes

Please provide a summary of the changes, including:

- Enable user to add custom JAVA ops with env JAVA_CUSTOM_OPTS
- Added support for prometheus (enabled via JAVA_CUSTOM_OPTS +
enterprise license)
- Changed settings from enterprise naming to 'Premium'
- KeygenLicense Check to support offline licenses
- Disable URL-to-PDF due to huge security bug
- Remove loud Split PDF logs
- addUsers renamed to adminSettings
- Added Usage analytics page
- Add user button to only be enabled based on total users free
- Improve Merge memory usage


Closes #(issue_number)

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing)
for more details.

---------

Co-authored-by: a <a>
Co-authored-by: pixeebot[bot] <104101892+pixeebot[bot]@users.noreply.github.com>
Co-authored-by: Connor Yoh <con.yoh13@gmail.com>

src/main/java/stirling/software/SPDF/EE/LicenseKeyChecker.java

@@ -1,6 +1,9 @@
 package stirling.software.SPDF.EE;
 
 import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.scheduling.annotation.Scheduled;
@@ -15,11 +18,13 @@ import stirling.software.SPDF.utils.GeneralUtils;
 @Slf4j
 public class LicenseKeyChecker {
 
+    private static final String FILE_PREFIX = "file:";
+
     private final KeygenLicenseVerifier licenseService;
 
     private final ApplicationProperties applicationProperties;
 
-    private boolean enterpriseEnabledResult = false;
+    private boolean premiumEnabledResult = false;
 
     @Autowired
     public LicenseKeyChecker(
@@ -35,27 +40,58 @@ public class LicenseKeyChecker {
     }
 
     private void checkLicense() {
-        if (!applicationProperties.getEnterpriseEdition().isEnabled()) {
-            enterpriseEnabledResult = false;
+        if (!applicationProperties.getPremium().isEnabled()) {
+            premiumEnabledResult = false;
         } else {
-            enterpriseEnabledResult =
-                    licenseService.verifyLicense(
-                            applicationProperties.getEnterpriseEdition().getKey());
-            if (enterpriseEnabledResult) {
-                log.info("License key is valid.");
+            String licenseKey = getLicenseKeyContent(applicationProperties.getPremium().getKey());
+            if (licenseKey != null) {
+                premiumEnabledResult = licenseService.verifyLicense(licenseKey);
+                if (premiumEnabledResult) {
+                    log.info("License key is valid.");
+                } else {
+                    log.info("License key is invalid.");
+                }
             } else {
-                log.info("License key is invalid.");
+                log.error("Failed to obtain license key content.");
+                premiumEnabledResult = false;
             }
         }
     }
 
+    private String getLicenseKeyContent(String keyOrFilePath) {
+        if (keyOrFilePath == null || keyOrFilePath.trim().isEmpty()) {
+            log.error("License key is not specified");
+            return null;
+        }
+
+        // Check if it's a file reference
+        if (keyOrFilePath.startsWith(FILE_PREFIX)) {
+            String filePath = keyOrFilePath.substring(FILE_PREFIX.length());
+            try {
+                Path path = Paths.get(filePath);
+                if (!Files.exists(path)) {
+                    log.error("License file does not exist: {}", filePath);
+                    return null;
+                }
+                log.info("Reading license from file: {}", filePath);
+                return Files.readString(path);
+            } catch (IOException e) {
+                log.error("Failed to read license file: {}", e.getMessage());
+                return null;
+            }
+        }
+
+        // It's a direct license key
+        return keyOrFilePath;
+    }
+
     public void updateLicenseKey(String newKey) throws IOException {
-        applicationProperties.getEnterpriseEdition().setKey(newKey);
+        applicationProperties.getPremium().setKey(newKey);
         GeneralUtils.saveKeyToSettings("EnterpriseEdition.key", newKey);
         checkLicense();
     }
 
     public boolean getEnterpriseEnabledResult() {
-        return enterpriseEnabledResult;
+        return premiumEnabledResult;
     }
 }