Incoherent naming for additional domainNames variable (code vs. documentation)

[mmoscher]

Helm-Chart and CRD documentations mentions a additionalDomainNames variable to provide further domainNames.
However, the CRD itself parses additionalDomains only.

[HoustonPutman]

The approach we have to take (for back-compat as well as rules around minor & patch releases) is:

• For v0.5.1 update the documentation (Fix documentation and example for additionalDomains #415)
• For v0.6.0 add the new field, and auto-populate with the value from the old field. Add upgrade notes, deprecate the old field. (Rename additionalDomains to additionalDomainNames #416)
• For v0.7.0 remove the old field from the CRD

[mmoscher]

@HoustonPutman thanks for taking over. I was the last week (unfortunately 😄 ) on vacation and therefore could not take care of it.

Thank you!