Add OAuth 2.0 support and token caching for Garmin

[this-Aditya]

This PR introduces the following updates:

• Updated GarminAuthValidator to verify OAuth 2.0 tokens.
• Migrated Garmin backfill requests from OAuth 1.0 signed requests to OAuth 2.0 bearer token authentication.
• Added a TokenCache to cache OAuth 2.0 access tokens.
  • OAuth 1.0 access tokens for Garmin do not expire and could be reused indefinitely once fetched.
  • OAuth 2.0 access tokens expire, so a this cache mechanism is added.
  • Tokens are cached only if their remaining lifetime is greater than 30 minutes to avoid expiration-related issues.

NOTE: This PR doesn't remove the support for oauth1, any version can be used by updating the configurations, once we fully migrate to oauth2 the oauth1 flow will be removed

[dosubot]

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