Fix config file save logic in FileBasedMessageStore

Previously, the `saveConfiguredMessage()` method was calling
`configFile.load()` after updating the config values with addAll(),
which reloaded the file from disk and discarded all in-memory changes.
This resulted in config updates being lost while only the HTML file was
saved.

Fix this by removing the `configFile.load()` call ensuring that
configuration changes are properly persisted to the config file along
with the HTML content.

Change-Id: I60dd739e6e74802437164ef218ef98eb0afdf0f7