feat: Add git pull support

[ZPascal]

Add pull input — pull before push support

Summary

Adds an optional pull input that performs a git pull before the push step.
This prevents push failures caused by diverged histories, especially in workflows
where multiple jobs or runners commit to the same branch concurrently.

fix: #84

TODO:

• Test the functionality

[Copilot]

Pull request overview

Adds an optional pull input to the GitHub Push Action so it can integrate upstream changes (git pull) right before pushing, reducing push failures when multiple runners/jobs update the same branch.

Changes:

• Introduces pull input with selectable strategies (rebase, merge, ff-only, true).
• Updates start.sh to run a pull step before the existing push step.
• Documents the new input and provides a workflow example in the README.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
start.sh	Adds conditional pre-push pull logic with strategy selection and remote URL construction.
README.md	Documents the new pull input and adds an example workflow showing usage.
action.yml	Exposes the new pull input (default false) in the action metadata.

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