Convert start new MR from Toggle to Checkbox
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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

## 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."
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