Add migration to backfill user_project_member_roles table

What does this MR do and why?

Backfill user_project_member_roles to record member role assignments for members of groups invited to projects (i.e. project_group_links).

For example,

1. Group Group adds Alice as a Developer
2. Project Proj invites Group as Guest + read_runners
3. Alice should have { user: Alice, project: Proj, shared_with_group: Group } user_project_member_roles record

References

Backfill user_project_member_roles for shared p... (#573551)

Database

Per sub-batch query

EXPLAIN: https://console.postgres.ai/shared/21c1bdc3-d3b5-482f-b62f-82dfb43e23fe

Screenshots or screen recordings

Before	After

How to set up and validate locally

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.