feat: run a terraform plan before creating workspaces with the given template parameters (#1732)

coderd/database/migrations/000099_provisioner_job_type_dry_run.down.sql

@@ -0,0 +1,9 @@
+-- It's not possible to drop enum values from enum types, so the UP has "IF NOT
+-- EXISTS".
+
+-- Delete all jobs that use the new enum value.
+DELETE FROM
+    provisioner_jobs
+WHERE
+    type = 'template_version_dry_run'
+;

coderd/database/migrations/000099_provisioner_job_type_dry_run.up.sql

@@ -0,0 +1,2 @@
+ALTER TYPE provisioner_job_type
+ADD VALUE IF NOT EXISTS 'template_version_dry_run';