OpenViking is_available() only consulted env vars and use_ovcli_config, so an
endpoint saved to config.yaml (e.g. by the Dashboard) reported needs_config;
_resolve_connection_settings() likewise never folded config.yaml's non-secret
fields into its chain. RetainDB initialize() read base_url/project from the
environment only, ignoring the values the Dashboard writes to config.yaml.
Both now resolve non-secret fields as env -> (ovcli ->) config.yaml -> default;
secrets still come from the environment. Adds regression tests for both.
Fixes#68209
(cherry picked from commit dca57915b97b5705b30927a062e1d0f2f23d3841)
PRATHAMESH75
5396dd8f02