Add github action to release helm charts

[kvaps]

Add github action to create chart releases automatically once the chart version is bumped.
After this PR and creation of orphan branch named gh-pages - this repository could be used in helm repo add command.

helm repo add nfs-ganesha-server-and-external-provisioner https://kubernetes-sigs.github.io/nfs-ganesha-server-and-external-provisioner/

For example, my fork can be used:

$ helm repo add nfs-ganesha-server-and-external-provisioner https://kvaps.github.io/nfs-ganesha-server-and-external-provisioner/
"nfs-ganesha-server-and-external-provisioner" has been added to your repositories
$ helm search repo
NAME                                           	CHART VERSION	APP VERSION	DESCRIPTION                                       
nfs-ganesha-server-and-external-provisioner/nfs...	1.3.2             	3.0.0             	nfs-server-provisioner is an out-of-tree dynami...

To create the gh-pages branch use: git checkout --orphan gh-pages.

[consideRatio]

Perhaps helm repo update required here also?

[consideRatio]

I've stopped doing this and rely on --repo flags when doing helm install or helm upgrade so I've forgotten.

[consideRatio]

Besides a documentation comment, this LGTM!

[kmova]

@kvaps - the gh-pages branch is pushed. I am good with this PR. Would you like me to go ahead or wait for resolving the minor doc comment.

[kmova]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: consideRatio, kmova, kvaps

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [kmova,kvaps]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment