Autogenerate secrets if no Helm value provided, remove insecure defaults

[arm4b]

In Helm values we specify unsafe defaults for SSL auto-generated cert #6, SSH key, st2 password to bring a "one click" experience.

An alternative to that is to auto-generate these secrets if no Helm values provided.

[arm4b]

Surprisingly, helm via Spring templating engine has a lot of crypto functions: https://masterminds.github.io/sprig/crypto.html
genPrivateKey and genSelfSignedCert is all we need.

So technically it's all possible, just a matter of implementation.

[arm4b]

As described in #62, Helm doesn't have enough functionality to transition from autogenerated vs custom values-defined state and so SSH key in Helm values remains as is until better instrumentation from Helm introduced.

We however can get rid of st2web/nginx SSL certificates from Helm values switching to HTTP by default and allow user to configure HTTPS as optional Ingress controller on top of st2web, - the plan defined in #6

[arm4b]

Per helm/helm#3053 (comment) looks like Helm3 has a new solution via new lookup feature.
We'll need to review this.

See https://helm.sh/docs/chart_template_guide/functions_and_pipelines/#using-the-lookup-function