Multiple public keys

[h2zh]

This issue is the continuation of #561

We want to allow multiple active private keys in use, which means there will be multiple public keys in JWKS.

1. CRUD operations for public keys management in Registry DB
2. Ensure director can use multiple public keys in the JWKS
3. Key management in Pelican client

[h2zh]

Feature 1,2 are done in PR #1748. Work on Feature 3 will begin after that PR is merged to avoid potential rework from any subsequent changes.

[h2zh]

This issue is replaced by these ones #1748 (review)