[Angular-Apollo-Tailwind] Add filters milestones on PRs

[iansamz]

Wont Resolve: #605

Unlike issues, pull requests do not have the $filterby parameter and hence it is not possible to filter by milestones.

For more information: https://docs.github.com/en/graphql/reference/objects#repository

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Filters on PRs don't include Milestones (but they do on issues page).

Acceptance

• Add Milestones to PRs filters so they can be aligned with the issues page.

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