ResourceManager -> ObjectManager (#548)

The ResourceManager type is split into an interface (ObjectManager) and
implementing struct (UpdatingObjectManager).

AggregateReconciler, ChildReconciler and ChildSetReconciler are updated
to allow specifying an alternative strategy with fallbacks to the previous
behavior.

Backwards compatibility is preserved with a number of deprecations,
including:

- `ResourceManager` is deprecated in favor of `ObjectManager` for a
   generic type, or `UpdatingObjectManager`.
- `AggregateReconciler.{HarmonizeImmutableFields, MergeBeforeUpdate,
   Sanitize}` are deprecated in favor of `AggregateReconciler.
   AggregateObjectManager`.
- `ChildReconciler.{Finalizer, HarmonizeImmutableFields,
   MergeBeforeUpdate, Sanitize, SetResourceManager}` are deprecated in
   favor of `ChildReconciler.ChildObjectManager`.
- `ChildSetReconciler.{HarmonizeImmutableFields, MergeBeforeUpdate,
   Sanitize}` are deprecated in favor of `ChildSetReconciler.
   ChildObjectManager`.

Other strategies can be provided in the future, like replacing Update()
calls with server-side apply.

Signed-off-by: Scott Andrews <[email protected]>

Merge pull request #540 from scothis/custom-defaulter

Apply defaults to objects implementing CustomDefaulter

Merge pull request #539 from reconcilerio/dependabot/go_modules/hack/…

…sigs.k8s.io/controller-tools-0.16.1

Bump sigs.k8s.io/controller-tools from 0.16.0 to 0.16.1 in /hack

Mark cutover commit

Signed-off-by: Scott Andrews <[email protected]>

List children exactly once for ChildSetReconciler (#494)

Previously, the ChildSetReconciler would list children once for the
set and again for each child being reconciled. At best this was
inefficient, at worst it introduced subtile issues when the content of
the listing changed over the course of the reconcile.

Now the content of the list from the ChildSetReconciler is reused by
each child that is reconciled.

Signed-off-by: Scott Andrews <[email protected]>

Bump sigs.k8s.io/controller-runtime from 0.17.1 to 0.17.2 (#483)

Bumps [sigs.k8s.io/controller-runtime](https://github.com/kubernetes-sigs/controller-runtime) from 0.17.1 to 0.17.2.
- [Release notes](https://github.com/kubernetes-sigs/controller-runtime/releases)
- [Changelog](https://github.com/kubernetes-sigs/controller-runtime/blob/main/RELEASE.md)
- [Commits](kubernetes-sigs/controller-runtime@v0.17.1...v0.17.2)

---
updated-dependencies:
- dependency-name: sigs.k8s.io/controller-runtime
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Bump github.com/evanphx/json-patch/v5 from 5.8.1 to 5.9.0 (#475)

Bumps [github.com/evanphx/json-patch/v5](https://github.com/evanphx/json-patch) from 5.8.1 to 5.9.0.
- [Release notes](https://github.com/evanphx/json-patch/releases)
- [Commits](evanphx/json-patch@v5.8.1...v5.9.0)

---
updated-dependencies:
- dependency-name: github.com/evanphx/json-patch/v5
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Add MAINTAINERS.md (#465)

Signed-off-by: Max Brauer <[email protected]>

Switch ResourceManager update cache to JSON Patch (#442)

It was previously using JSON Merge Patch, which will recreate structures
that are trying to be deleted. JSON Patch will fail to apply the patch
if the structure being patched doesn't exist.

For example, if a reconciler defined a volume on a Deployment on
create/update a mutating webhook will default the file permissions. If
the reconciler later needs to remove that volume, the defaulted file
permissions will no longer be re-applied.

Signed-off-by: Scott Andrews <[email protected]>

Streamline finalizer patching (#434)

Since the client can now handle duck type resources, we no longer need
to cast the current resources back to the parent resource type.

Signed-off-by: Scott Andrews <[email protected]>