Fixes#6
### Motivation
As suggested here: https://pulsar.apache.org/docs/en/helm-deploy/#prepare-the-helm-release. The ```prepare_helm_release.sh``` script provided with this Helm chart can create a secret credentials resource and
> The username and password are used for logging into Grafana dashboard and Pulsar Manager.
However, I haven't been able to make use of such a feature for a number of reasons:
1. This secret doesn't seem to affect the ```pulsar-manager-deployment.yaml``` definition. Instead, the ```./templates/pulsar-manager-admin-secret.yaml``` seems to be the one providing the credentials for the pulsar manager (UI) (with the added possibility to overwrite via values.yaml at ```pulsar_manager.admin.user/password```).
2. Using the Pulsar chart as a dependency for an umbrella chart (this is currently my use case), will bring extra hassle that will make it very hard to have all resources follow the same naming structure, thus causing some resources to never be deployed successfully e.g.: ```./templates/grafana-deployment.yaml``` will complain that it couldn't find the secret created by the bash script. Attempting to fix this issue via the ```-k``` flag passed to the script will cause the JWT secret tokens to have a name that's unexpected by the broker, etc.
### Modifications
Decouple grafana credentials from pulsar manager via a new secret resource named ```./charts/pulsar/templates/grafana-admin-secret.yaml```.
Add credentials overriding via values.yaml in the same way as pulsar_manager (grafana.admin.user/password) & delete secret resource manipulation from bash scripts (cleaup_helm_release.sh & prepare_helm_release.sh)
### Verifying this change
- [x] Make sure that the change passes the CI checks.
### Motivation
While making use of the scripts provided in this repo to prepare helm releases, I noticed that providing the ```-d``` flag (delete namespace) for the ```./scripts/pulsar/cleanup_helm_release.sh``` would always fail claiming that the **namespace already exists**. Upon closer examination, I noticed that the kubectl command to delete the provided namespace is actually attempting to create it instead.
### Modifications
I've gone ahead and made the corresponding modification on the script to delete the namespace (went from ```kubectl create namespace ${namespace}``` to ```kubectl delete namespace ${namespace}```).
### Verifying this change
I'm not sure what possible verifications I can provide for this PR. Please advise.
