feat(coderd): add support for external agents to API's and provisioner (#19286)

This pull request introduces support for external workspace management, allowing users to register and manage workspaces that are provisioned and managed outside of the Coder.

Depends on: https://github.com/coder/terraform-provider-coder/pull/424

* GET /api/v2/init-script - Gets the agent initialization script
  * By default, it returns a script for Linux (amd64), but with query parameters (os and arch) you can get the init script for different platforms
* GET /api/v2/workspaces/{workspace}/external-agent/{agent}/credentials - Gets credentials for an external agent **(enterprise)**
* Updated queries to filter workspaces/templates by the has_external_agent field

coderd/provisionerdserver/provisionerdserver.go

@@ -1733,11 +1733,14 @@ func (s *server) completeTemplateImportJob(ctx context.Context, job database.Pro
 				Bool:  jobType.TemplateImport.HasAiTasks,
 				Valid: true,
 			},
-			HasExternalAgent: sql.NullBool{},
-			UpdatedAt:        now,
+			HasExternalAgent: sql.NullBool{
+				Bool:  jobType.TemplateImport.HasExternalAgents,
+				Valid: true,
+			},
+			UpdatedAt: now,
 		})
 		if err != nil {
-			return xerrors.Errorf("update template version external auth providers: %w", err)
+			return xerrors.Errorf("update template version ai task and external agent: %w", err)
 		}
 
 		// Process terraform values
@@ -2027,6 +2030,14 @@ func (s *server) completeWorkspaceBuildJob(ctx context.Context, job database.Pro
 			sidebarAppID = uuid.NullUUID{}
 		}
 
+		hasExternalAgent := false
+		for _, resource := range jobType.WorkspaceBuild.Resources {
+			if resource.Type == "coder_external_agent" {
+				hasExternalAgent = true
+				break
+			}
+		}
+
 		// Regardless of whether there is an AI task or not, update the field to indicate one way or the other since it
 		// always defaults to nil. ONLY if has_ai_task=true MUST ai_task_sidebar_app_id be set.
 		if err := db.UpdateWorkspaceBuildFlagsByID(ctx, database.UpdateWorkspaceBuildFlagsByIDParams{
@@ -2035,11 +2046,14 @@ func (s *server) completeWorkspaceBuildJob(ctx context.Context, job database.Pro
 				Bool:  hasAITask,
 				Valid: true,
 			},
-			HasExternalAgent: sql.NullBool{},
-			SidebarAppID:     sidebarAppID,
-			UpdatedAt:        now,
+			HasExternalAgent: sql.NullBool{
+				Bool:  hasExternalAgent,
+				Valid: true,
+			},
+			SidebarAppID: sidebarAppID,
+			UpdatedAt:    now,
 		}); err != nil {
-			return xerrors.Errorf("update workspace build ai tasks flag: %w", err)
+			return xerrors.Errorf("update workspace build ai tasks and external agent flag: %w", err)
 		}
 
 		// Insert timings inside the transaction now