[improvement]: Remove configure from main branches, have release process produce configure for tag and tarball

[jcolp]

Improvement Description

Per discussion on the asterisk-dev mailing list to reduce churn when configure changes are made, and to reduce our conflicts if we have multiple configure changes going on the following will be done:

1. 'configure' will be removed from the mainline branches (18, 20, master)
2. Documentation will be updated with instructions for running bootstrap.sh in this scenario
3. Makefile will state that configure needs to be run if it has not already been done and is invoked
4. The release process will be updated to run bootstrap.sh and produce the configure script, this configure script will be placed in the tag and release tarball
5. The CI process will be updated to include running bootstrap.sh as part of the build process
6. Add to .gitignore in mainline branches

[gtjoseph]

One problem...
If you're on 18 with configure removed and you run bootstrap, then switch to releases/18 git overwrites your local configure as it should. if you switch back to 18 however, configure is deleted since it's not in that index and you have to run bootstrap again.

[jcolp]

I don't see that as a problem. If you're changing to any mainline branch you should rerun bootstrap.sh

[lathama]

Add to gitignore also?