This adds a connection string repo, where connection strings can be stored.
The general idea is that it is possible to store connection strings, say an S3 connection, and then re-use the connection string for multiple backups, editing as needed.
The implementation supports listing connection strings, creating, updating, and deleting them.
The connection strings are masked so sensitive information is not available in the browser, and the logic patches connection strings internally to ensure markers are replaced with the correct values.
The connection string itself is stored in full, such that a Duplicati version roll-back will not make the connectionstring become invalid.
There is also an endpoint that allows updating existing backups using the connection string, so it is easy to rotate keys. The logic for this feature is that it retains: scheme, port, host, path, and any extra settings on the target url.
It does not remove settings from the target, but will overwrite or add settings from the connectionstring.
This PR adds the ability to manage backup configurations outside of the the client.
The implementation ensures that locally created configurations cannot be affected by the remotely managed backups.
If the instance is not connected to a remote console, this has no effect.
This PR updates the local database to add the column `ExternalID` that tracks backups that are managed remotely.
Kenneth Skovhede