Unable to Update the SSH Base Url from bitbucket.properties file if already set via Server settings in GUI

Issue Summary

Once you've set an SSH base URL in the UI, you are unable to un-set it so the value from the bitbucket.properties is used. If you delete the UI value, Bitbucket Server will use the default (instead of using any value in bitbucket. properties).

Change the UI behaviour so deleting the value in the UI will completely clear the set value in the DB so that the value in bitbucket.properties will be used (as if the user had never set a value in the UI).

Note: That the UI has higher priority than the bitbucket.properties file is not the issue... the issue is that it is impossible to un-set the UI value so the system looks at the bitbucket.properties file.

Steps to Reproduce

1. Update the SSH base URL via Server Setting GUI
2. then delete the value of the SSH base URL from the GUI and try to add it from the bitbucket.properties file as given below and restart the bitbucket service

   plugin.ssh.baseurl=ssh://git@localhost:5740
   

   Expected Results

   Bitbucket should take the value mentioned in the bitbucket.properties file

   Actual Results

   It ignores the value in the bitbucket.properties file and sets the SSH base URL to default
   So, once the SSH base URL is set via GUI there is no way to modify it via the bitbucket.properties file
   The below exception is thrown in the xxxxxxx.log file:

   atlassian-bitbucket.log:2020-08-04 19:20:15,433 WARN  [spring-startup]  c.a.b.ssh.SshConfigurationService Application configuration property 'plugin.ssh.baseurl' is not used because its value has been configured in the Server settings
   

   Workaround

   there is currently no way to modify the base url rather than from GUI