[DOP-39515] Cache keycloak keys

[TiGrib]

Change Summary

Cache keycloak keys

Related issue number

[DOP-39515]

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[github-actions]

Coverage Report •

File	Stmts	Miss	Branch	BrPart	Cover	Missing
syncmaster/server/providers/auth
keycloak_provider.py	102	17	14	3	83%	65, 82–84, 118–120, 122->123, 123–124, 130->131, 131–132, 160->161, 161–162, 166–169
TOTAL	5360	635	830	171	87%