feat: support pulling by a specific commit or a date

[OmarIthawi]

Currently the atlas pull supports a --branch argument which accepts only git branches and tags.

atlas pull could be more verstile if it supported a more generic --revision argument which could accept the following revisions:

• Git branch e.g. git checkout open-release/quince.master
• Git tag e.g. git checkout open-release/quince.1
• Git commit SHA git checkout f098hab11
• Git branch at a specific date git checkout 'main@{2020-11-06}' as supported by https://linux.die.net/man/1/git-rev-parse