Ability to specify additional CA using a secret name/key

[divolgin]

What this PR does / why we need it:

In addition to using a configmap to provide SDK with custom CA, this allows using a secret. Example values:

privateCASecret:
  name: additional-ca
  key: custom-ca.crt

This is a follow up to #209

Which issue(s) this PR fixes:

Fixes https://app.shortcut.com/replicated/story/113584/can-t-reuse-existing-secret-for-custom-ca

Special notes for your reviewer:

Steps to reproduce

Does this PR introduce a user-facing change?

Adds support for specifying custom Certificate Authorities using a secret.

Does this PR require documentation?

replicatedhq/replicated-docs#2742

[ggguardian]

Nice Job!
IMO It could be interesting to provide the CA directly in the values without relying on an existing ConfigMap/Secret though as it is not something really sensitive.
A use case would be for a user to provide a CA file via KOTS config, and we could inject that value into the replicated Helm chart’s values, for example, What do you think?

I suggest adding the following parameter in values:

privateCA: |
    <certificate>

[divolgin]

Nice Job! IMO It could be interesting to provide the CA directly in the values without relying on an existing ConfigMap/Secret though as it is not something really sensitive. A use case would be for a user to provide a CA file via KOTS config, and we could inject that value into the replicated Helm chart’s values, for example, What do you think?

I suggest adding the following parameter in values:

privateCA: |
    <certificate>

That makes sense. This behavior would need some parity with KOTS. I'm going to go ahead and merge this since this satisfies your requirements. Just to remind you that if you need anything, there is a Feature Request option on the support form