mgr/prometheus: extend tls config to work with Rook orch

mgr/prometheus: extend tls config to work with Rook orch

This commit extends tls to work with Rook orch that has been deployed for cephadm.

Certificates are read from rook namespace via kubernetes api client.
Name of the secrets are provided by following parameter:

prometheus_tls_secret_name (default secret name "rook-ceph-prometheus-server-tls")

When cephadm is used it generates silf signed certificates, when
rook used it reads certififcates from kubernetes client api in rook_env.namespace.

Signed-off-by: Sunnatillo <sunnat.samadov@est.tech>