[CLI] Add support for preparing GB patch releases

[jhnstn]

Fixes #153

This updates the prepare gb command to accept patch versions (e.g. 1.1071) and a prs flag to pass a comma separated list of PRs on gutenberg

If the command recognizes a patch release it will branch of the prior release and then attempt cherry pick the merge commits from the passed in PRs.

If there is a merge commit the script will prompt to resolve the merge commit in the users default $EDITOR. if EDITOR is not set, the script will prompt for a command to open the conflicting files (e.g. vim or code )

Once the branch is prepared the script will prompt to edit the changelog since the changelog might not accurately reflect the changes in the patch.

Testing

This is difficult to completely verify with out getting noisy on the Gutenberg repo. Also this is difficult to set up on forked repos. I suggest using the WordPress/gutenberg to test but just make sure to exit the script when prompted to create the pr i.e. a this prompt "Ready to create the PR on WordPress/gutenberg? [y/n]"

I also found it is easier to verify the scripts correctness by trying to recreate existing patch releases.

Testing with merge conflicts

• Run GBM_WORDPRESS_ORG=WordPress go run main.go release prepare gb 1.103.2 --no-tag --prs=54281 to recreate the 1.103.2 release (use the --no-tag just in case the PR does get created)
• Follow the prompts to resolve any merge conflicts
• Follow the prompts to correctly update the CHANGELOG
• Note the commits to be included in the PR when the preview is presented
• Exit the script without creating the PR

Testing with multiple PRs

• Run GBM_WORDPRESS_ORG=WordPress go run main.go release prepare gb 1.103.2 --no-tag --prs=54281,54096
• Follow the same prompts as above but you should get two merge conflicts
• Note that both PR commits are listed in the commits in the PR list
• Exit the script without creating the PR

Verifying the branching (also test with out merge conflicts)

• Run GBM_WORDPRESS_ORG=WordPress go run main.go release prepare gb 1.107.1 --prs=55613 --no-tag --keep
• Note that the only prompt is to verify the change log (as of the time of this pr creation, the could change)
• Exit the script without creating the PR
• cd into the temporary directory
• Run git reflog
• Note that the log history starts on a grafted branch at the tag rnmobile/1.107.0 It should look something like :

  d6311ae (HEAD -> rnmobile/release_1.107.1) HEAD@{0}: commit: Release script: Update podfile
  6451ed7 HEAD@{1}: reset: moving to HEAD
  6451ed7 HEAD@{2}: commit: Release script: Update CHANGELOG for version 1.107.1
  b7c4eb7 HEAD@{3}: commit: Release script: Update react-native-editor version to 1.107.1
  f84d2b8 HEAD@{4}: cherry-pick: [RNMobile] Fix error when pasting deeply nested structure content (#55613)
  1c3a1ac (grafted, tag: rnmobile/1.107.0) HEAD@{5}: checkout: moving from 1c3a1ac5b7add6ed335787e9770dc59b0c9d8d6b to rnmobile/release_1.107.1
  1c3a1ac (grafted, tag: rnmobile/1.107.0) HEAD@{6}: clone: from github.com:WordPress/gutenberg

Testing the editor prompt

• Run EDITOR= GBM_WORDPRESS_ORG=WordPress go run main.go release prepare gb 1.107.1 --prs=55613 --no-tag to nil out $EDITOR
• Note the prompt to provide a command to open the change log
• Try using any text editor that can open files from the command line e.g. vim, code or nano
• Note that the correct file from the temp directory is opened in the chosen editor

Regression

• Verify that the script works as expected for scheduled releases (this can easily be tested against a fork of gutenberg)

Note : There is no verification that a merge conflict was correctly resolved. I suspect most conflicts will be in the change notes so the last verification step should surface any issues with that file.

Note: The editor prompts have only been tested with vim,code and nano but in theory any command that takes a list of files should work.

[jhnstn]

Looks good! I was able to run through all of the patch scenarios successfully. I think I encountered a regression with the prepare all command, however:

➜ yes | GBM_WPMOBILE_ORG=derekblank GBM_WORDPRESS_ORG=derekblank go run main.go release prepare all 1.110.0
[INFO] Preparing Gutenberg for release 1.110.0
[INFO] Cloning Gutenberg to /var/folders/xk/xmtl5xjx33v_bp94749wm0j00000gn/T/gbm-2609010841/gb
Cloning into '.'...
warning: Could not find remote branch  to clone.
fatal: Remote branch  not found in upstream origin
[ERROR] error cloning the Gutenberg repository: exit status 128

This happens on both the main repos and my forked repos. I think this might be coming from build.Base.Ref. Is prepare all still a command, or should we run them individually as gb and gbm? If we're running them individually, we should remove all and update the docs.

Ah thanks for checking that @derekblank ! I forgot to update the all command. I can push a fix.

[jhnstn]

@derekblank I fixed the regression in https://github.com/wordpress-mobile/release-toolkit-gutenberg-mobile/pull/212/commits/696857cbc0f2f1859b26ebb875da6acdde82abad