feat: graduate prebuilds to general availability (#18607)

This PR removes the prebuilds experiment and allows the use of prebuilds
without opting into an experiment.

coderd/apidoc/swagger.json

@@ -10927,15 +10927,13 @@
 				"auto-fill-parameters",
 				"notifications",
 				"workspace-usage",
-				"web-push",
-				"workspace-prebuilds"
+				"web-push"
 			],
 			"x-enum-comments": {
 				"ExperimentAutoFillParameters": "This should not be taken out of experiments until we have redesigned the feature.",
 				"ExperimentExample": "This isn't used for anything.",
 				"ExperimentNotifications": "Sends notifications via SMTP and webhooks following certain events.",
 				"ExperimentWebPush": "Enables web push notifications through the browser.",
-				"ExperimentWorkspacePrebuilds": "Enables the new workspace prebuilds feature.",
 				"ExperimentWorkspaceUsage": "Enables the new workspace usage tracking."
 			},
 			"x-enum-varnames": [
@@ -10943,8 +10941,7 @@
 				"ExperimentAutoFillParameters",
 				"ExperimentNotifications",
 				"ExperimentWorkspaceUsage",
-				"ExperimentWebPush",
-				"ExperimentWorkspacePrebuilds"
+				"ExperimentWebPush"
 			]
 		},
 		"codersdk.ExternalAuth": {