fix: pepr mutation annotation overwrite (#385)

## Description
Fixes the overwriting of previous pepr mutation annotations by merging
them.

## Related Issue

Fixes #
<!-- or -->
Relates to #

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Other (security config, docs update, etc)

## Checklist before merging

- [x] Test, docs, adr added or updated as needed
- [ ] [Contributor Guide
Steps](https://github.com/defenseunicorns/uds-template-capability/blob/main/CONTRIBUTING.md)(https://github.com/defenseunicorns/uds-template-capability/blob/main/CONTRIBUTING.md#submitting-a-pull-request)
followed

Co-authored-by: Micah Nagel <micah.nagel@defenseunicorns.com>

src/pepr/policies/common.ts

@@ -103,5 +103,10 @@ export function annotateMutation<T extends KubernetesObject>(
   request: PeprMutateRequest<T>,
   policy: Policy,
 ) {
-  request.SetAnnotation(`uds-core.pepr.dev/mutated`, transform(policy));
+  const key = "uds-core.pepr.dev/mutated";
+  const annotations = request.Raw.metadata?.annotations ?? {};
+  const valStr = annotations[key];
+  const arr = JSON.parse(valStr || "[]");
+  arr.push(transform(policy));
+  request.SetAnnotation(key, JSON.stringify(arr));
 }