Add editing of meal donations.

[jho426]

Notion Ticket Link

Replace with Ticket URL

Implementation Description

• Implemented the UpdateMealRequestDonation mutation which allows a user to modify the meal_description and additional_info fields of their donation
• Added a new test for the mutation

Steps To Test

1. Run make betest

What Should Reviewers Focus On?

• The logic and functionality of the code

Checklist

• [✅ ] My PR name is descriptive and in imperative tense
• [✅ ] My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• [ ✅] I have run the appropriate linter(s)
• [ ✅] I have added tests for my changes
• [ ✅] I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

[github-actions]

Visit the preview URL for this PR (updated for commit af0e267):

https://feeding-canadian-kids-staging--pr126-jho426-update-req-otnr1nqb.web.app

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[shahanneda]

Thanks for working on this Jacqueline! Congrats on your first BE ticket. Since I was working on donor onsite contacts, I went ahead and added them to this branch, and so I just finished up the PR, so no more work from you is needed for this! Though feel free to improve the form further if you have ideas.