[MINT-3259] Allow linking milestone on add common solution

[OddTomBrooks]

MINT-3259

Description

This PR allows for adding milestone links when adding common solutions

How to test this change

1. Run scripts/dev test:go and validate unit test success
2. Run Postman endpoint to add common solution and validate that milestone links are added as expected

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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