feat: add option to enable auto-merge pull requests

[r4vn]

Introduces an auto-merge input to the version action. This input enables auto-merging via squashing for the created pull request when set to true.

Please note that it will only enable auto-merge, if the repository allows it, squash merging is enabled and has branch protection rules set up.

Example:

jobs:
  version:
    runs-on: ubuntu-latest
    steps:
      - name: Version
        uses: ExodusMovement/lerna-release-action/version@master
        with:
          github-token: ${{ secrets.GH_AUTOMATION_PAT }}
          packages: ${{ inputs.packages }}
          assignee: ${{ inputs.assignee }}
          version-strategy: ${{ inputs.version-strategy }}
          auto-merge: true

Closes #20

[sparten11740]

@r4vn can we enable in hydra please 🙏🏼