[ENG-11076][eas-cli] prompt user to map channel on update if unmapped

[quinlanj]

Why

When an update is created with the channel flag, it will error if the channel is not mapped to a branch.

> eas update --channel main
Channel has no branches associated with it. Run 'eas channel:edit' to map a branch

This PR allows the user to select the branch to map in this case:

>  eas-dev update --channel blah
Channel has no branches associated with it.
✔ Which branch would you like blah to point at? › gh/quinlanj/3/orig

Test Plan

• amended test to expect new behaviour

[linear]

ENG-11076 eas update: auto create branch if channel has no branches

[github-actions]

Size Change: -365 B (0%)

Total Size: 50.2 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	50.2 MB	-365 B (0%)

_{compressed-size-action}

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (e9064b7) 54.11% compared to head (377c7a9) 54.12%.

Files	Patch %	Lines
...li/src/update/getBranchNameFromChannelNameAsync.ts	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2185      +/-   ##
==========================================
+ Coverage   54.11%   54.12%   +0.02%     
==========================================
  Files         516      516              
  Lines       18815    18822       +7     
  Branches     3771     3771              
==========================================
+ Hits        10179    10185       +6     
- Misses       8615     8616       +1     
  Partials       21       21              

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[quinlanj]

/changelog-entry chore prompt user to map channel on update if unmapped

[github-actions]

✅ Thank you for adding the changelog entry!

[wschurman]

It feels awkward to me that we allow creating an update with just a channel flag since updates are associated with branches instead of channels. I assume the channel flag was added as a convenience flag for singly-mapped channel-branch combinations?

edit: PR that added it makes it seem like this behavior might have been intentional: #1567
cc @jonsamp

[wschurman]

I guess my other worry is that this might be too heavy of an operation for people to comprehend what is being done. By pointing an existing channel at an existing branch, any other/existing builds with that channel will now receive compatible updates on that branch. I worry that people running a simple eas update command may not comprehend the potential magnitude of such an operation and may just answer "yes" out of habit, which could have unintended consequences in production.

[wschurman]

Requesting changes for now to put it back in your queue to assess.

[quinlanj]

@wschurman you raise a really good point in #2185 (comment) . People will have to select a branch to map to a channel (they don't reply y), but I agree someone could just be pressing the Return key out of habit, not expecting that some variant of eas update would change the mapping of their channel.

Closing this PR to retain the original behaviour.