Ability to provide own certificate for gRPC channel in Bamboo datacenter

Currently Bamboo Datacenter uses a self signed certificate for the ssl gRPC communication between nodes within the cluster. Bamboo will listen on the node.internal.communication.port port [9090] for the gRPC traffic. This leads some security scanners to complain that this is insecure as the issuer is not a known CA.

The following certificate was at the top of the certificate
chain sent by the remote host, but it is signed by an unknown
certificate authority :

|-Subject : CN=Local node
|-Issuer : CN=Bamboo GRPC Root CA

Affected Port:
9090/tcp

If the certificate does not exist then Bamboo will recreate a self-signed certificate when a cluster node is started.

This request is to allow the Bamboo admin to provide their own certificate with CA of their choice rather than a self signed certificate.