docs(redis-ha): Introduce helm-docs for values documentation

[mkilchhofer]

What this PR does / why we need it:

Manually ensuring proper documentation for all parameters is almost impossible and also in this redis-ha helm chart a plenty of variables were undocumented.

The helper utility helm-docs has a wide adoption inside CNCF projects.

Which issue this PR fixes

none

Special notes for your reviewer:

I already templated the chart before my change and after my change

$ helm template . > rendered-master.yaml

$ git co -
Switched to branch 'feature/redis-ha_introduce_helm-docs'
Your branch is up to date with 'origin/feature/redis-ha_introduce_helm-docs'.

$ helm template . > rendered-feature_redis-ha_introduce_helm-docs.yaml

$ diff -u rendered-master.yaml rendered-feature_redis-ha_introduce_helm-docs.yaml
$ echo $?
0

This should verify that we do not introduce a regression with this docs change.

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• DCO signed
• Chart Version bumped
• Variables are documented in the README.md
• Title of the PR starts with chart name (e.g. [stable/mychartname])

[DandyDeveloper]

Helm docs is new to me! Let me go through this quickly so I can approve knowing I'm up to speed!

[mkilchhofer]

@DandyDeveloper friendly reminder

[mkilchhofer]

@DandyDeveloper another friendly ping

[DandyDeveloper]

I am here! Just neglected my duties this past couple of months. Sorry!