feat: Enable passing a specific version number to release-please (#128)

This will save me so much time going and editing PRs to get the desired
version number.

If not specified, Release Please will determine the next version like it
always does.

Examples of me using it:
hedia-team/hedia-server#500

.github/workflows/release-please.yml

@@ -22,6 +22,10 @@ on:
                 required: false
                 default: false
                 type: boolean
+            version:
+                description: Specific version number to release, eg '3.0.0' or '3.1.0-rc.0'. If not provided, Release Please will determine the version.
+                required: false
+                type: string
 
         outputs:
             release_created:
@@ -60,6 +64,7 @@ jobs:
                   token: ${{ secrets.HEDIA_BOT_GITHUB_PAT }}
                   default-branch: ${{ github.ref_name }}
                   changelog-types: '[{"type":"feat","section":"New Features","hidden":false},{"type":"fix","section":"Bug Fixes","hidden":false},{"type":"revert","section":"Reverted Changes","hidden":false},{"type":"perf","section":"Performance Improvements","hidden":false},{"type":"refactor","section":"Code Refactoring","hidden":false},{"type":"build","section":"Build Process","hidden":false},{"type":"ci","section":"CI/CD","hidden":false},{"type":"test","section":"Testing","hidden":false},{"type":"chore","section":"Chores","hidden":false},{"type":"docs","section":"Documentation Updates","hidden":false},{"type":"style","section":"Code Formatting","hidden":false}]'
+                  release-as: ${{ inputs.version || '' }}
 
         outputs:
             release_created: ${{ steps.release-please.outputs.release_created }}