feat(coderd/agentapi): implement sub agent api (#17823)

Closes https://github.com/coder/internal/issues/619

Implement the `coderd` side of the AgentAPI for the upcoming
dev-container agents work.

`agent/agenttest/client.go` is left unimplemented for a future PR
working to implement the agent side of this feature.

coderd/database/queries.sql.go

@@ -14159,6 +14159,15 @@ func (q *sqlQuerier) DeleteOldWorkspaceAgentLogs(ctx context.Context, threshold
 	return err
 }
 
+const deleteWorkspaceSubAgentByID = `-- name: DeleteWorkspaceSubAgentByID :exec
+DELETE FROM workspace_agents WHERE id = $1 AND parent_id IS NOT NULL
+`
+
+func (q *sqlQuerier) DeleteWorkspaceSubAgentByID(ctx context.Context, id uuid.UUID) error {
+	_, err := q.db.ExecContext(ctx, deleteWorkspaceSubAgentByID, id)
+	return err
+}
+
 const getWorkspaceAgentAndLatestBuildByAuthToken = `-- name: GetWorkspaceAgentAndLatestBuildByAuthToken :one
 SELECT
 	workspaces.id, workspaces.created_at, workspaces.updated_at, workspaces.owner_id, workspaces.organization_id, workspaces.template_id, workspaces.deleted, workspaces.name, workspaces.autostart_schedule, workspaces.ttl, workspaces.last_used_at, workspaces.dormant_at, workspaces.deleting_at, workspaces.automatic_updates, workspaces.favorite, workspaces.next_start_at,
@@ -14591,6 +14600,67 @@ func (q *sqlQuerier) GetWorkspaceAgentScriptTimingsByBuildID(ctx context.Context
 	return items, nil
 }
 
+const getWorkspaceAgentsByParentID = `-- name: GetWorkspaceAgentsByParentID :many
+SELECT id, created_at, updated_at, name, first_connected_at, last_connected_at, disconnected_at, resource_id, auth_token, auth_instance_id, architecture, environment_variables, operating_system, instance_metadata, resource_metadata, directory, version, last_connected_replica_id, connection_timeout_seconds, troubleshooting_url, motd_file, lifecycle_state, expanded_directory, logs_length, logs_overflowed, started_at, ready_at, subsystems, display_apps, api_version, display_order, parent_id, api_key_scope FROM workspace_agents WHERE parent_id = $1::uuid
+`
+
+func (q *sqlQuerier) GetWorkspaceAgentsByParentID(ctx context.Context, parentID uuid.UUID) ([]WorkspaceAgent, error) {
+	rows, err := q.db.QueryContext(ctx, getWorkspaceAgentsByParentID, parentID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []WorkspaceAgent
+	for rows.Next() {
+		var i WorkspaceAgent
+		if err := rows.Scan(
+			&i.ID,
+			&i.CreatedAt,
+			&i.UpdatedAt,
+			&i.Name,
+			&i.FirstConnectedAt,
+			&i.LastConnectedAt,
+			&i.DisconnectedAt,
+			&i.ResourceID,
+			&i.AuthToken,
+			&i.AuthInstanceID,
+			&i.Architecture,
+			&i.EnvironmentVariables,
+			&i.OperatingSystem,
+			&i.InstanceMetadata,
+			&i.ResourceMetadata,
+			&i.Directory,
+			&i.Version,
+			&i.LastConnectedReplicaID,
+			&i.ConnectionTimeoutSeconds,
+			&i.TroubleshootingURL,
+			&i.MOTDFile,
+			&i.LifecycleState,
+			&i.ExpandedDirectory,
+			&i.LogsLength,
+			&i.LogsOverflowed,
+			&i.StartedAt,
+			&i.ReadyAt,
+			pq.Array(&i.Subsystems),
+			pq.Array(&i.DisplayApps),
+			&i.APIVersion,
+			&i.DisplayOrder,
+			&i.ParentID,
+			&i.APIKeyScope,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Close(); err != nil {
+		return nil, err
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const getWorkspaceAgentsByResourceIDs = `-- name: GetWorkspaceAgentsByResourceIDs :many
 SELECT
 	id, created_at, updated_at, name, first_connected_at, last_connected_at, disconnected_at, resource_id, auth_token, auth_instance_id, architecture, environment_variables, operating_system, instance_metadata, resource_metadata, directory, version, last_connected_replica_id, connection_timeout_seconds, troubleshooting_url, motd_file, lifecycle_state, expanded_directory, logs_length, logs_overflowed, started_at, ready_at, subsystems, display_apps, api_version, display_order, parent_id, api_key_scope