feat(create-and-merge-pull-request): support configurable merge methods

[neilime]

Summary

This makes actions/create-and-merge-pull-request configurable for repositories that cannot use rebase merges, while keeping the current default behavior unchanged.

Changes

• add a new merge-method input with merge, rebase, and squash values
• keep rebase as the default to preserve existing behavior
• add optional merge-commit-title and merge-commit-message inputs for merge and squash flows
• document the new inputs in the action README
• update the root action catalog description to reflect configurable merge behavior

Motivation

On repositories that require signed commits on the base branch, GitHub refuses automatic rebase merges with errors like:

GraphQL: Base branch requires signed commits. Rebase merges cannot be automatically signed by GitHub

This change lets consumers switch to merge-method: squash while still using the shared action.

Validation

• reviewed the generated upstream diff after push
• confirmed the merge flags against gh pr merge --help and GitHub CLI documentation

Notes

This keeps the action opinionated, but removes the hardcoded rebase-only behavior that breaks protected branches with signed-commit requirements.

[github-actions]

Super-linter summary

Language	Validation result
BIOME_FORMAT	Pass ✅
BIOME_LINT	Pass ✅
CHECKOV	Pass ✅
GITHUB_ACTIONS_ZIZMOR	Pass ✅
GITLEAKS	Pass ✅
GIT_MERGE_CONFLICT_MARKERS	Pass ✅
JSCPD	Pass ✅
MARKDOWN	Pass ✅
MARKDOWN_PRETTIER	Pass ✅
NATURAL_LANGUAGE	Pass ✅
PRE_COMMIT	Pass ✅
SPELL_CODESPELL	Pass ✅
TRIVY	Pass ✅
YAML	Pass ✅
YAML_PRETTIER	Pass ✅

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[github-actions]

Super-linter summary

Language	Validation result
BIOME_FORMAT	Pass ✅
BIOME_LINT	Pass ✅
CHECKOV	Pass ✅
GITHUB_ACTIONS_ZIZMOR	Pass ✅
GITLEAKS	Pass ✅
GIT_MERGE_CONFLICT_MARKERS	Pass ✅
JSCPD	Pass ✅
MARKDOWN	Pass ✅
MARKDOWN_PRETTIER	Pass ✅
NATURAL_LANGUAGE	Pass ✅
PRE_COMMIT	Pass ✅
SPELL_CODESPELL	Pass ✅
TRIVY	Pass ✅
YAML	Pass ✅
YAML_PRETTIER	Pass ✅

All files and directories linted successfully

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[github-actions]

Super-linter summary

Language	Validation result
BIOME_FORMAT	Pass ✅
BIOME_LINT	Pass ✅
CHECKOV	Pass ✅
GITHUB_ACTIONS_ZIZMOR	Pass ✅
GITLEAKS	Pass ✅
GIT_MERGE_CONFLICT_MARKERS	Pass ✅
JSCPD	Pass ✅
MARKDOWN	Pass ✅
MARKDOWN_PRETTIER	Pass ✅
NATURAL_LANGUAGE	Pass ✅
PRE_COMMIT	Pass ✅
SPELL_CODESPELL	Pass ✅
TRIVY	Pass ✅
YAML	Pass ✅
YAML_PRETTIER	Pass ✅

All files and directories linted successfully

For more information, see the GitHub Actions workflow run

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