tlsSecret.extraServerCerts property was added to be able to mount certs

[andrewdevelopz]

When using Kafka it would be nice to be able to include additional certs into /etc/certs/server directory.

This branch adds a tlsSecret.extraServerCerts property that allows adding additional sources of certs.

So if values.yaml is like below:

tlsSecret:
  name: "fleet-telemetry-secret"
  extraServerCerts:
    - secret:
        name: cluster-ca-cert
        items:
          - key: ca.crt
            path: ca.crt
    - secret:
        name: kafka-user
        items:
          - key: user.crt
            path: kafka.crt
          - key: user.key
            path: kafka.key

Then 2-deployment.yaml will produce in volumes:

      - name: server-certs
        projected:
          sources:
          - secret:
              name: fleet-telemetry-secret
          - secret:
              items:
              - key: ca.crt
                path: ca.crt
              name: cluster-ca-cert
          - secret:
              items:
              - key: user.crt
                path: kafka.crt
              - key: user.key
                path: kafka.key
              name: kafka-user

This way, configs for fleet-telemetry can be sent to k8s like below:

    {
      "host": "0.0.0.0",
      "port": 443,
      ...
      "kafka": {
          "bootstrap.servers": "<bootstrap-url>",
          "security.protocol": "SSL",
          "ssl.ca.location": "/etc/certs/server/ca.crt",
          "ssl.certificate.location": "/etc/certs/server/kafka.crt",
          "ssl.key.location": "/etc/certs/server/kafka.key"
      },
      "tls": {
        "server_cert": "/etc/certs/server/tls.crt",
        "server_key": "/etc/certs/server/tls.key"
      }
    }