[Authentication][MSAL] Document the platform support matrix for MSAL and UNO_EXT_MSAL usage

[kazo0]

As of this, we now need to wrap the MSAL builder calls with UNO_EXT_MSAL. Like we are doing in the TestHarness.

We should document the platforms that are/are not supported and highlight the usage of UNO_EXT_MSAL in the MSAL How-to docs