Convert start new MR from Toggle to Checkbox
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Work on this issue](https://contributors.gitlab.com/manage-issue?action=work&projectId=278964&issueIid=342195) - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=342195) </details> <!--IssueSummary end--> Let's update the modal with "Start new merge request" to use a checkbox instead of a toggle. - Replace blob modal - Delete blob modal - New directory modal - Upload file modal <img src="/uploads/1c35fa35960ddd0547f9df32cd2bc24d/image.png" height="300px"> This will make it match the IDE ![image](/uploads/f22c90c3760537a41b20388ea37825ca/image.png) ## Background Info The following discussion from !71154 should be addressed: - [ ] `@mnichols1` started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/71154#note_690615760): (+2 comments) > I noticed the start a new merge request option was changed from a checkbox to a toggle switch. I think we may want to stick with the checkbox. I think the toggle meets the [when to use](https://design.gitlab.com/components/toggle#use-a-toggle-when-) of being binary and having a default state, but I think "The result of changing the toggle state is immediately effective" is what makes the checkbox the better choice. Also under the [do not use section](https://design.gitlab.com/components/toggle#do-not-use-a-toggle-when-) "When the setting exists within a form that has other elements, like text inputs or checkboxes, that need to be saved or submitted." > > ![image](https://gitlab.com/gitlab-org/gitlab/uploads/09f795e0dccc7d613a216f6dcd35f769/image.png)
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