[Feature]: provide the bumping level as output of the actions

[ricogu]

Feature: expose SemVer bump level as action output

Problem

This action determines the required SemVer bump level (major / minor / patch) from the PR title and runs on pull_request events.

In some ecosystems (e.g. Go), the project version is not stored in a file, but derived from git tags.
As a result, the action cannot (and should not) update a version during the PR itself.
However, the computed bump level is still valuable information for downstream automation within the same workflow.

Currently, this bump decision is internal to the action and cannot be reused by consumers.

Proposal

Expose the computed SemVer bump level as a GitHub Actions output:

• bump: one of major | minor | patch
  (always set, since every PR must map to a bump level)

This output should directly reflect the result of the existing PR-title parsing logic.

Example usage

- name: Determine SemVer bump from PR title
  id: semver
  uses: SAP/pull-request-semver-bumper@v1

- name: Consume bump level
  run: echo "Bump level is ${{ steps.semver.outputs.bump }}"

Benefits

• Makes the action more composable and reusable
• Allows consumers to drive PR-time automation based on the bump level
• Supports workflows where versioning and tagging are handled outside the PR

Acceptance criteria

• Action exposes bump as an output (major | minor | patch)
• Output is documented in the README
• Existing behavior remains unchanged (additive feature)

[ricogu]

@mdanish98, does the description make sense for you?