perf: reduce calls to GetWorkspaceByAgentID in GetWorkspaceAgentByID (#21046)

This PR piggy backs on the agent API cached workspace added in an earlier PR to provide a fast path for avoiding `GetWorkspaceByAgentID` calls in dbauthz's `GetWorkspaceAgentByID`. This query is not the most expensive, but has a significant call volume at ~16 million calls per week.

Signed-off-by: Callum Styan <callumstyan@gmail.com>

coderd/agentapi/api.go

@@ -197,6 +197,7 @@ func New(opts Options, workspace database.Workspace) *API {
 		AgentFn:          api.agent,
 		ConnectionLogger: opts.ConnectionLogger,
 		Database:         opts.Database,
+		Workspace:        api.cachedWorkspaceFields,
 		Log:              opts.Log,
 	}