Frontend file upload

[keiferms3]

Proposed changes

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Created a new form to create container autograders and added a file upload field to the submission creation form. Added postMultipart and putMultipart functions to RequestService to make multipart-form requests.

Types of changes

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What types of changes does your code introduce? Put an x in the boxes that apply

• [x] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation Update (if none of the other choices apply)

Checklist

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Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. This is simply a reminder of what we are going to look for before merging your code.

• [x] My changeset covers only what is described above (no extraneous changes)
• [x] Lint and unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)

Further comments

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As an assignment can only have a single container autograder, a way to update CAGs should be implemented on the frontend.

Notable bug, as the handling of query parameters has changed on this route's backend, the assignment detail page currently displays every submission on every assignment's page.

[jessehartloff]

I merged this before noticing there was a conversation.. These comments should still be addressed in another PR @keiferms3