Migrate app/assets/javascripts/projects/commits/store/index.js to Pinia

app/assets/javascripts/projects/commits/store/index.js store should be migrated to Pinia using the single-step migration.

Files to cover (non-exhaustive):

• app/assets/javascripts/projects/commits/store/index.js
• app/assets/javascripts/projects/commits/store/actions.js
• app/assets/javascripts/projects/commits/store/mutations.js
• app/assets/javascripts/projects/commits/store/state.js
• app/assets/javascripts/projects/commits/index.js
• app/assets/javascripts/projects/commits/components/author_select.vue

And their respective specs.