[MINT-3229]milestone category resolvers and milestone by ID

[StevenWadeOddball]

MINT-3229

Description

1. This implemented a resolver to return a new parent level MTOCategories type on an MTO milestone
   a. After syncing, we decided to rely on a parent level call and a dataloader to focus on simple maintainable code, instead of creating a more complicated dataloader that would return both records and deserialize.
2. Syncing with the FE team, it was determined we should also be able to get a milestone by ID, so we don't have to call this category resolver when we are looking at all milestones for the model

How to test this change

Use the postman queries to

1. Create an MTO milestone
2. Get the MTO milestone by ID
3. Verify the Categories information for the milestone.
   a. note a nil category will return uncategorized uncategorized

PR Author Checklist

• I have provided a detailed description of the changes in this PR.
• I have provided clear instructions on how to test the changes in this PR.
• I have updated tests or written new tests as appropriate in this PR.
• Updated the Postman Collection if necessary.

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[ClayBenson94]

I've left a few points of feedback and some suggestions -- mainly around TODO comments, other code comments, and function naming. Nothing too major, IMO!

[StevenWadeOddball]

Thanks for the feedback Clay! Changes should be implemented :D

[ClayBenson94]

Changes look good to me! This should help unblock most of the FE for the edit milestone modal! 🚀