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/searchquery/search_test.go

@@ -252,6 +252,36 @@ func TestSearchWorkspace(t *testing.T) {
 				},
 			},
 		},
+		{
+			Name:  "HasExternalAgentTrue",
+			Query: "has_external_agent:true",
+			Expected: database.GetWorkspacesParams{
+				HasExternalAgent: sql.NullBool{
+					Bool:  true,
+					Valid: true,
+				},
+			},
+		},
+		{
+			Name:  "HasExternalAgentFalse",
+			Query: "has_external_agent:false",
+			Expected: database.GetWorkspacesParams{
+				HasExternalAgent: sql.NullBool{
+					Bool:  false,
+					Valid: true,
+				},
+			},
+		},
+		{
+			Name:  "HasExternalAgentMissing",
+			Query: "",
+			Expected: database.GetWorkspacesParams{
+				HasExternalAgent: sql.NullBool{
+					Bool:  false,
+					Valid: false,
+				},
+			},
+		},
 
 		// Failures
 		{
@@ -689,6 +719,36 @@ func TestSearchTemplates(t *testing.T) {
 				},
 			},
 		},
+		{
+			Name:  "HasExternalAgent",
+			Query: "has_external_agent:true",
+			Expected: database.GetTemplatesWithFilterParams{
+				HasExternalAgent: sql.NullBool{
+					Bool:  true,
+					Valid: true,
+				},
+			},
+		},
+		{
+			Name:  "HasExternalAgentFalse",
+			Query: "has_external_agent:false",
+			Expected: database.GetTemplatesWithFilterParams{
+				HasExternalAgent: sql.NullBool{
+					Bool:  false,
+					Valid: true,
+				},
+			},
+		},
+		{
+			Name:  "HasExternalAgentMissing",
+			Query: "",
+			Expected: database.GetTemplatesWithFilterParams{
+				HasExternalAgent: sql.NullBool{
+					Bool:  false,
+					Valid: false,
+				},
+			},
+		},
 		{
 			Name:  "MyTemplates",
 			Query: "author:me",