[RFC] Create supported branch from edk2-stable* tag (Required to address critical bug BZ3111)

["Michael D Kinney" <michael.d.kinney@intel.com>]

Hello,

The following bug has been fixed on edk2/master

    https://bugzilla.tianocore.org/show_bug.cgi?id=3111
    https://github.com/tianocore/edk2/pull/1226

This bug is also considered a critical bug against edk2-stable202011.  The behavior
of the Variable Lock Protocol was changed in a non-backwards compatible manner in
edk2-stable202011 and this is impacting some downstream platforms.  The following
2 commits on edk2/master restore the original behavior of the Variable Lock Protocol.

    https://github.com/tianocore/edk2/pull/1226/commits/893cfe2847b83da74f53858d6acaa15a348bad7c
    https://github.com/tianocore/edk2/pull/1226/commits/16491ba6a6e9a91cedeeed45bc0fbdfde49f7968

The request here is to create a supported branch from edk2-stable202011 tag and apply 
these 2 commits as critical bug fixes on the supported branch.

Since we started using the edk2-stable* tag process, there has not been a request to create
a supported branch from one of those tags.  As a result, there are a couple opens that 
need to be addressed:

1) Supported branch naming convention.

    Proposal: stable/edk2-stable*
    Example:  stable/edk2-stable202011

2) CI requirements for supported branches.

    Proposal: Update .azurepipelines yml files to also trigger on stable/* branches
    and update GitHub settings so stable/* branches are protected branches.

3) Release requirements for supported branches.

   Proposal: If there are a significant number of critical fixes applied to
   a stable/edk2-stable* branch, then a request for a release can be made that
   would trigger focused testing of the supported branch and creation of a new
   release.  If all testing passes, then a tag is created on the stable/edk2-stable*
   branch and a release is created on GitHub that summarizes the set of critical
   fixes and the testing performed.

   Proposal: edk2-stable<YYYY><MM>.<XX> 
   Example : edk2-stable201111.01

Please let me know if you have any feedback or comments on this proposal.  The goal
is to close on this topic this week.
  
Thank you,

Mike