FR: Enhance aliases to run multiple commands with conditional logic

[kuchta]

If aliases would be able to run multiple commands with conditional logic, many workflow specific commands (porcelain in git jargon) could be implemented by the user or his/her company.

Many current commands expect some idiomatic workflow which could be implemented as a default aliases if aliases allow for conditional logic and new command eg. is-same-revision <revision> <revision>

This change would externalize such workflow specific commands (and discussions) to user configurable defaults and be potentionaly replaced by user/company preferred workflow...

[PhilipMetzger]

This FR is probably a subset of #3262, as it is along the static/dynamic configuration discussion, which has been brought up many times in Discord.

[fowles]

I actually just ran across this myself. I would very much like an alias that lets me do jj branch set main -r @- && jj git push -b main. Bonus points for allowing it to take the branch name as an argument or to figure it out from the log.