Fix connection at init for commandlets

[SRombautsU]

When the Editor run a Commandlet from the command line, it does trigger a ISourceControlProvider::Login() so there is no "Connect" operation and the Plastic SCM plugin doesn't check the connectivity to the server

The plugin is fully functional, but it will report otherwise in PlasticSourceControlProvider::IsAvaillable() returning false

This will fail all methods of USourceControlHelpers like CheckOutOrAddFile() that will stop at SourceControlHelpersInternal::VerifySourceControl()

Fix FPlasticSourceControlProvider::Init() to respect bForceConnection, executing a 'checkconnection' command to set bServerAvailable based on the connectivity of the server

[SRombautsU]

Running a ResaveDirtyPackage test commandlet added to our development project

Before:

.\Tools\SaveDirtyPackagesCommandlet.bat
[2022.05.12-14.36.26:348][  0]LogInit: Display: Warning/Error Summary (Unique only)
[2022.05.12-14.36.26:348][  0]LogInit: Display: -----------------------------------
[2022.05.12-14.36.26:348][  0]LogInit: Display: SourceControl: Error: Source control server is currently not available.
[2022.05.12-14.36.26:348][  0]LogInit: Display: LogSaveDirtyPackagesCommandlet: Error: Cannot checkout C:/Workspace/UE5PlasticPluginDev/Content/Characters/Mannequins/Animations/Manny/MM_Fall_Loop.uasset
[2022.05.12-14.36.26:348][  0]LogInit: Display: LogSaveDirtyPackagesCommandlet: Error: Cannot checkout C:/Workspace/UE5PlasticPluginDev/Content/Characters/Mannequins/Animations/Manny/MM_Idle.uasset
[...]
[2022.05.12-14.36.26:349][  0]LogInit: Display: LogSaveDirtyPackagesCommandlet: Error: Cannot checkin

After:

[2022.05.12-14.39.54:537][  0]LogInit: Display:
[2022.05.12-14.39.54:537][  0]LogInit: Display: Success - 0 error(s), 0 warning(s)
[2022.05.12-14.39.54:537][  0]LogInit: Display:
Execution of commandlet took:  1.37 seconds