Adapt the shell script to build releases and release note with the new tagging model

[amaltaro]

Impact of the new feature
WMCore

Is your feature request related to a problem? Please describe.
As discussed over the last few weeks, we are making PyPi and WMCore versioning consistent, basically deprecating pre and patch releases. Further information can be found here:
https://github.com/dmwm/WMCore/wiki/TaggingAndReleasing#new-tagging-convention

Describe the solution you'd like
Update our shell script to create a new WMCore tag and build the release notes:
https://github.com/dmwm/WMCore/blob/master/bin/buildrelease.sh

such that it starts considering the rc (release candidate) tags and the 4 digit tags (meant to be used as patch version now).

Describe alternatives you've considered
None

Additional context
None