Support multiple wildcard certificate domains

[arsenetar]

Describe the feature

Add ability to have multiple wildcard certificate domains. Currently only the default domain creates per namespace wildcard certificates. Would like the ability to specify multiple wildcard domains. Proposed method would be to flag the domains in the domain config to mark them as wildcard:

    example.com: |
      wildcard: true
      selector:
        app: secret

This format should be reverse compatible with the existing configuration. The default domain still would use wildcard, but would allow potentially for disabling wildcard for the default domain if desired.

I have an initial version of code that provides this functionality from the configuration loading, and the actual wildcard certificate creation.

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[dprotaso]

/assign @arsenetar
/triage accepted