Add support for some reconnect and disconnect detection options

Added some options from CLI version and added an option for fixed reconnect_interval from my MR to CLI version: openconnect!590

Please review the TODO strings in src/vpninfo.cpp to correctly determine the proper API version.

In the current version of OpenConnect-GUI, if you restart the server, all clients will disconnect and will not attempt to reconnect automatically. The second commit "Add support for reconnect after disconnect from server" is proposed to fix this behavior.

! I cannot run the pipelines because I am unable to verify my account due to my telephone number not being accepted.

Checklist

• Code modified for feature
• Documentation updated / CHANGELOG.md entry present (for non-trivial changes)

Reviewer's checklist:

• Any issues marked for closing are addressed
• Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTING.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code