Fix pipeline allow_duplicate_names never converges (#6076)

## Changes

Declare pipeline `allow_duplicate_names` as `input_only` in
`ignore_remote_changes`, next to the existing `run_as` entry. Adds a
`no_drift` invariant config covering it.

## Why

The field is only carried by `CreatePipeline`/`EditPipeline` and is
never returned by GET, so remote always reads back `false`. With
`allow_duplicate_names: true`, every plan after a deploy reported a
perpetual update (`old: true, new: true` — config unchanged, phantom
remote drift). It's in `RemoteType` via the embedded `CreatePipeline`,
so the automatic `missing_in_remote` suppression doesn't apply.

`dry_run` is request-only in the same way, but `EditPipeline` has no
`DryRun` field, so it needs its own fix and is out of scope here.

## Tests

New `pipeline_allow_duplicate_names.yml.tmpl` invariant config: fails on
`main`, passes with the fix. Also confirmed on dogfood — perpetual `1 to
change` across three deploys before the fix, control pipeline without
the field clean.

Author: radakam

.nextchanges/bundles/pipeline-allow-duplicate-names-converges.md

@@ -0,0 +1 @@
+Fixed a pipeline with `allow_duplicate_names: true` never converging on the direct engine: the field is only accepted on create/update and is never returned by the pipelines GET API, so every subsequent `bundle plan` reported the pipeline as a perpetual update.

acceptance/bundle/invariant/configs/pipeline_allow_duplicate_names.yml.tmpl

@@ -0,0 +1,11 @@
+bundle:
+  name: test-bundle-$UNIQUE_NAME
+
+resources:
+  pipelines:
+    foo:
+      name: test-pipeline-$UNIQUE_NAME
+      allow_duplicate_names: true
+      libraries:
+        - file:
+            path: pipeline.py

acceptance/bundle/invariant/continue_293/out.test.toml

@@ -49,6 +49,7 @@ EnvMatrix.INPUT_CONFIG = [
     "model_with_permissions.yml.tmpl",
     "model_serving_endpoint.yml.tmpl",
     "pipeline.yml.tmpl",
+    "pipeline_allow_duplicate_names.yml.tmpl",
     "pipeline_apply_policy_default_values.yml.tmpl",
     "pipeline_config_dots.yml.tmpl",
     "postgres_branch.yml.tmpl",

acceptance/bundle/invariant/delete_idempotent/out.test.toml

@@ -180,6 +180,10 @@ resources:
         reason: "!drop"
       - field: run_as
         reason: input_only
+      # Carried by CreatePipeline/EditPipeline but never returned by GET, so remote
+      # always reads back false and a config value of true never converges.
+      - field: allow_duplicate_names
+        reason: input_only
 
     ignore_local_changes:
       - field: deployment.version_id