Support k8s secrets in console pod

[cniackz]

To fix: #1439

Explanation:

In the certificate path we only look for public.crt and private.key to serve console in 9443. But in k8s we have other type of secrets with different file names like cert-manager secrets or k8s secrets, hence we should also support tls.crt and tls.key to allow people to use cert-manager or other methods not just our self-signed cert.

How to test:

1. k proxy
2. IntelliJ or other tool with this run/debug config:

How it looks:

$ pwd
/Users/cniackz/.console/certs

$ ls
CAs		tls.crt		tls.key

GOROOT=/usr/local/go #gosetup
GOPATH=/Users/cniackz/go #gosetup
/usr/local/go/bin/go build -trimpath -o /Users/cniackz/operator/go_build_github_com_minio_operator_cmd_operator . #gosetup
/Users/cniackz/operator/go_build_github_com_minio_operator_cmd_operator ui
Serving operator at http://[::]:9090
Serving operator at https://[::]:9443

Expected:

Serving operator at https://[::]:9443 <---- Meaning you are serving on HTTPS on that particular pod.

[jiuker]

LGTM

[cniackz]

Thank you guys!