Add customizable commitMessage config option for change and publish

[Copilot]

Adds a commitMessage config function so the git commit message for change and publish can be customized, including dynamic content like version numbers via the provided context. (Previously only publish could be customized via the --message CLI arg with a static string.)

Changes

• RepoOptions.commitMessage: new optional function (options, packageInfos, bumpInfo?) => string | Promise<string>. bumpInfo (and post-bump packageInfos) are only supplied for publish.
• change: resolves commitMessage for the change-files commit; defaults to 'Change files'.
• publish: commit message precedence is now --message/message config → commitMessage() → default 'applying package updates'. The default was moved from cli.ts into publish() so it no longer masks commitMessage.
• Docs: added to configuration reference and CI integration guide.

Example

// beachball.config.js
module.exports = {
  commitMessage: (options, packageInfos, bumpInfo) =>
    bumpInfo
      ? `Release ${Object.keys(bumpInfo.modifiedPackages).length} packages [skip ci]`
      : 'Add change files',
};

[ecraig12345]

@copilot and also look at the previous comment