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

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

Files to cover (non-exhaustive):

• app/assets/javascripts/projects/commit/store/index.js
• app/assets/javascripts/projects/commit/store/actions.js
• app/assets/javascripts/projects/commit/store/getters.js
• app/assets/javascripts/projects/commit/store/mutations.js
• app/assets/javascripts/projects/commit/store/state.js
• app/assets/javascripts/projects/commit/init_cherry_pick_commit_modal.js
• app/assets/javascripts/projects/commit/init_revert_commit_modal.js
• app/assets/javascripts/projects/commit/components/projects_dropdown.vue
• app/assets/javascripts/projects/commit/components/branches_dropdown.vue
• app/assets/javascripts/projects/commit/components/form_modal.vue

And their respective specs.