Re-declare hashicorp/http provider to unblock existing workspace state

Removing the jetbrains module (previous commit) dropped the only thing in
these templates that used the hashicorp/http provider (the module fetched
IDE metadata via it internally). terraform init only installs providers the
current config declares, but any workspace whose state still has resources
from a template version that included the jetbrains module needs that
provider available to reconcile/destroy those entries - without it,
plan/apply fails with "Missing required provider ... hashicorp/http".

Re-declaring it in required_providers (all 6 templates) unblocks those
existing workspaces' next apply. Safe to remove again once every workspace
has updated past the jetbrains-module version.

templates/3d-printing/main.tf

@@ -6,6 +6,16 @@ terraform {
     docker = {
       source = "kreuzwerker/docker"
     }
+    # Not used directly in this config. Existing workspace state from before
+    # the jetbrains module was removed still has resources tagged under this
+    # provider (the module used it internally to fetch IDE metadata) -
+    # terraform init only installs providers the current config declares, so
+    # without this, plan/apply fails with "Missing required provider" while
+    # trying to reconcile/destroy those leftover state entries. Safe to drop
+    # once every workspace has updated past the jetbrains-module version.
+    http = {
+      source = "hashicorp/http"
+    }
   }
 }