Rename allowed-merge-apps to bypass-apps

[marcoieni]

Since we switched to rulesets, this makes more sense.
Note that triagebot reads the v1 api, so we should release this change in a backwards compatible way, updating their schema like we did in rust-lang/triagebot#2448

[cuba0001]

Ready for this.

[marcoieni]

the change of #2586 has been merged in triagebot in rust-lang/triagebot#2464
So we can remove the allowed-merge-apps field now