* Add support for advanced.config

- related to issue #219 
- configured through `spec.rabbitmq.advancedConfig` as
a string
- updating advancedConfig will trigger a sts rolling restart
bc similar to `rabbitmq.conf`, advanced config is loaded at
node start
- set maxLength for advancedConfig to 100000

Set RabbitMQ cluster name to CR name

Bump Dockerfile to latest ubuntu. The tag "latest" in Ubuntu Docker image means "Latest LTS".

* Add client service override `spec.override.clientService`

- this closes #142
- add an additional port example; using the client service override
- make sts and svc override's name and namespace not configurable

Remove private registry test

Add default annotations to all Pod templates

Removed a duplicated make target.

This test is too specific to a specific infrastructure setup. By testing
that we template the image pull secret correctly in the StatefulSet it
should give the same coverage as this test.

Pinning to a specific SHA no longer makes sense with no OSL process.

Updates the StatefulSet Pod template to always contain the prometheus
scrape annotations.

This allows users of the default Prometheus helm chart to automatically
scrape any RabbitMQ Pods created by this CR.

Link to doc guides on rabbitmq.com and local examples

* Add example about import definitions

- related to issue https://github.com/rabbitmq/cluster-operator/issues/104

Several fixes to statefulSet Override

- this is related to PR #175
- ObjectMeta.Labels and ObjectMeta.Annotations are merged when
patching instead of replace.

- this is related and a followup to feature in PR #175
- SetControllerReference should be called after override is applied since
the object's name and namespace could be modified by the override.
- delete the unit test which asserts that sts's ns can be overwritten
by override; the test is incorrect and will never pass, since
cluster-scoped resources (sts in this case), can not be owned by objects
in a other namespace.

Config for GitHub issues

Recommend to ask questions in either RabbitMQ Discussions or in the mailing list.

Prune unnecessary operator RBAC permissions

Update issue templates

Small readme changes

Remove boilerplate from bug report. Ask for relevant information to reproduce a bug in software.

We add RBAC permissions to the operator via generator annotations in
rabbitmqcluster_controller.go. The length of the feedback loop for
testing which are actually necessary (e.g. build an image, deploy to a
registry or kind, run all the tests against it) is long and haphazard.
Some roles are required by underlying structures (e.g. the listing and
watching functions in the Reflector) so it's not just a question of
checking what API calls we make in the Reconcile function.
Historically, this has resulted in us over provisioning.

- related to issue #143
- add reasoning about why the CRD won't install in a 1.18 k8s
cluster
- move Override KEP into proposals/implemented

- RabbitmqResourceBuilder is used sed in all tests in
internal/resource for the same purpose
- Use the same variable name for consistency

- we do not need to create a new sts builder in each test spec

- also update helm chart description

Remove deprecated `bases` from kustomization files

This addresses issue #183

* Add statefulSet override

- new crd properties: spec.override.statefulSet, which is
our own definition of appsv1.StatefulSet, which allows users to provide
a patch that will be applied on top of generated statefulset definition
as an override.
- new type EmbeddedObjectMeta, which is a partially metav1.ObjectMeta;
it is used in StatefulSet, PodTemplateSpec, and PersistentVolumeClaim.
- custom types are needed because of the pruning behavior of
`preserveUnknownFields: false`, which is going to be the default
behavior for crd v1.
- all fields in the custom StatefulSetSpec are optional; including
selector, serviceName...etc

`bases` is a deprecated section of the kustomize API, and is replaced by
`resources` in v2.1.0 onwards. Since we use kustomize 3.X, this moves
our kustomization yamls to the new accepted format.

This also moves our Makefile away from using `kubectl <apply/delete>
-k`, which uses kubectl's older, bundled version of Kustomize v2.0.3
(see [this issue](https://github.com/kubernetes/kubectl/issues/818)).