Microsoft OAuth2 for mailing on CloverDX Server

As follow-up on CLO-22666, it will be necessary to implement way to allow creation of OAuth2 token for server-side mailing (Configuration -> Setup -> Email).

Implementation may (as in case of jobs) support multiple vendors using generic configuration, just without any hinting for required scopes, URLs, etc.

It is expected, token will be email specific functionality and be defined globally for all server's automated mailing system (Alerts & Notifications, Event Listener and Schedule tasks).

Suggested implementation

Add dropdown to Authentication section of mailing configuration to select between possible authentication types:

Dropdown will determine, which fields are to be shown to fill in. Choosing OAuth2 (Microsoft) shows same fields are CloverDX Designer currently does when Azure option is chosen (Client ID, Tenant ID, Client Secret) to fill in, Scopes + all related URLs pre-filled with defaults required by service (Redirect URL = valid URL of connected server node, with same hostname and context address of browser window). Generic connector will offer empty input fields.

This new functionality should use as much of existing OAuth2 framework as possible.

Choosing any form of OAuth2 authentication, or change of credentials should change label of "Save" button to "Authenticate & Save". For authenticated connections, there will be another button "Re-Authenticate".

Retrieved tokens and configuration (specifically Client Secret) may be stored both in database or directly in clover.properties file, encrypted using Master password. Preference is to keep this information in file, solely for reason to be consistent with rest of server settings.