[ENG-11658][eas-cli] dont generate channel on `eas update` without flag

[quinlanj]

Why

An alternative solution to https://github.com/expo/eas-cli/pull/2339 , after talking to @jonsamp and @wschurman

When users create an update, we make sure that the branch they publish to is linked to a channel of the same name. However, this behaviour is not always desirable. For example, in the development usecase where someone is trying to load their update in the dev-client, a channel is not necesary. Users will either navigate to the update they want in the dev client menu or via a preview QR code.

How

• Only create a channel and link it to a branch when the --channel flag is passed

Test Plan

• [x] ensure eas update --channel bar creates channel bar, links it to branch bar, then publishes an update to the branch
• [x] ensure eas update:roll-back-to-embedded --channel bar creates channel bar, links it to branch bar, then publishes an update to the branch
• [x] ensure eas update --branch bar and eas update --auto no longer create a channel
• [x] - [ ] ensure eas update:roll-back-to-embedded --branch bar and eas update:roll-back-to-embedded --auto no longer create a channel

[quinlanj]

/changelog-entry breaking-change Stop creating a channel on eas update and eas update:roll-back-to-embedded unless the --channel flag is specified

[linear[bot]]

ENG-11658 Add a way to not create channel on update

[github-actions[bot]]

✅ Thank you for adding the changelog entry!

[github-actions[bot]]

Size Change: +2.96 kB (0%)

Total Size: 51.4 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	51.4 MB	+2.96 kB (0%)

_{compressed-size-action}

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 53.68%. Comparing base (d9092e1) to head (5cf760c). Report is 7 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2346 +/- ## ========================================== + Coverage 53.67% 53.68% +0.01% ========================================== Files 525 525 Lines 19268 19265 -3 Branches 4068 4066 -2 ========================================== Hits 10340 10340 + Misses 8203 8200 -3 Partials 725 725 ```

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[wschurman]

Related consequence of this: https://github.com/expo/expo/issues/29205. I think this is still the right call, but we'll need to audit the docs for local builds to ensure channels are manually created since they're no longer generated here.