feat!: only allow creation of one UDSPackage per namespace

[noahpb]

Description

This introduces a breaking change to the UDS Operator.

As part of our ongoing work to introduce ambient mesh support to UDS Core, we have made the decision to restrict consumers to creating one UDS Package custom resource in any given namespace. This PR introduces this change to the operator.

Notable changes:

• Adds a new Pepr watch for UDSPackage
• Adds a PackageStore intended to serve as an in-memory map of all namespaces that have packages
• Adds a check to package validator that will block the creation of a UDSPackage if there is a preexisting UDSPackage in the target namespace

This change has limited backwards compatibility. Users with namespaces that have one or more Package CR may be prevented from making additional modifications to their existing Package CRs. Delete actions against these Package CRs will never be blocked, but updates/patches can be. Users are encouraged to elect a single Package CR to remain in the namespace and migrate configurations accordingly.

Related Issue

Fixes #1352

Type of change

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

Steps to Validate

# check out this branch and then run:
$ uds run dev-setup

# deploy the operator
$ npx pepr deploy

# create a test package in a valid namespace:
$ kubectl create ns test
$ kubectl apply -f - <<EOF
apiVersion: uds.dev/v1alpha1
kind: Package
metadata:
  name: foo
  labels: {}
  namespace: test
spec: {}
EOF
package.uds.dev/foo created

# create a new package in the same namespace:
$ kubectl apply -f - <<EOF
apiVersion: uds.dev/v1alpha1
kind: Package
metadata:
  name: foo-1
  labels: {}
  namespace: test
spec: {}
EOF
Error from server: error when creating "STDIN": admission webhook "pepr-uds-core.pepr.dev" denied the request: A package with the name "foo" already exists in the namespace "test". Only one package can exist in a namespace.

# apply an update to the existing package
$ kubectl apply -f - <<EOF
apiVersion: uds.dev/v1alpha1
kind: Package
metadata:
  name: foo
  namespace: test
spec: {}
EOF
package.uds.dev/foo configured

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide followed

BEGIN_COMMIT_OVERRIDE
feat!: only allow creation of one UDSPackage per namespace (#1372)

BREAKING CHANGE: Package CR validation will now prevent creating multiple Package CRs in the same namespace. Ensure that you only have a single Package CR per namespace before this upgrade, otherwise you may be unable to update them going forward.
END_COMMIT_OVERRIDE

[slaskawi]

LGTM on my side

[mjnagel]

LGTM from a functional perspective. Two comments on cleaning/simplifying logic, but the current approach does work as well.