The purpose of this PR is to reduce the number of global_user_state.get_cluster_yaml_dict calls during handling of sky status.

Currently, global_user_state.get_cluster_yaml_dict is called once per backend_utils.ssh_credential_from_yaml, which is called in _update_record_with_credentials_and_resources_str. This function is called once per cluster. When an API server has many clusters, the number of DB calls increase linearly.

By renaming and refactoring _update_record_with_credentials_and_resources_str into _update_records_with_credentials_and_resources_str, we can allow the function to make a single db call to get all ssh credentials for the clusters. Appropriate changes are made in backend_utils.py and global_user_state.py to facilitate this change.

Testing: Testing is done entirely with smoke tests. Since sky status is one of the most comprehensively tested calls in smoke tests, smoke test should be enough to ensure lack of regression.

Tested (run the relevant ones):

• Code formatting: install pre-commit (auto-check on commit) or bash format.sh
• All smoke tests: /smoke-test (CI) or pytest tests/test_smoke.py (local)
• Backward compatibility: /quicktest-core (CI) or pytest tests/smoke_tests/test_backward_compat.py (local)