Upload new file modal: Replace toggle with commit changes UI

ℹ️ For latest discussion see: #444302 (comment 2192732639) and !170512 (merged)

Proposal

After discussions in #444302 (closed), the piece of UI that allows users to commit to a new/existing branch has been updated for the Edit/Delete file flow in !170512 (merged). This branch selection UI inside modals that allow users to commit changes should also be percolated to: New file, Upload file, and New directory. The design proposal is:

1. Replace the toggle for "Start a new merge request with these changes" with a checkbox as per Pajamas guidelines
2. Update the "Target branch" section of the UI to allow users to commit to the current branch, or new branch

Current	Proposed

Problem

When you go to upload a file, the option to start a merge request is a toggle.

Steps

1. Go to "Code > Repository"
2. Click on the "+"
3. Click on "Upload file"

Implementation guide

The same toggle is used in three places. That is:

1. new_directory_modal.vue
2. delete_blob_modal.vue
3. upload_blob_modal.vue

Change GlToggle to GlFormCheckbox

Scenarios

The following conditions should be considered (see !170512 (merged)):

• Commit to the current branch and user can push to the branch
• Commit to the current branch and user can NOT push to the branch
• Commit to new branch and open a MR
• Commit to new branch and NOT open a MR
• Cancel button pops a confirmation modal
• Mobile screen

Related UI

These are areas of the UI that should all be using the same commit changes modal UI:

UI element	Issues/MRs	Reproduction steps
Edit file	#444302 (closed) !170512 (merged) (reverted)	Code > Repository > Select a file > Edit > Edit single file
Delete file	#444302 (closed) !168992 (merged) #503405 (closed) (open)	Code > Repository > Select a file > Delete
New file	#502460 (closed) (open)	Code > Repository > New file
Upload file	#479249 (closed) (this, open)	Code > Repository > Upload file
New directory	#502483 (closed) (open)	Code > Repository > New directory