Support for APM server configuration

[nkvoll]

• apm server controller
• full support for APM configuration (see Support for APM server configuration #53 (comment))

[nkvoll]

APM server resource format suggestion snapshot (WIP)

apiVersion: apm.k8s.elastic.co/v1alpha1
kind: ApmServer
metadata:
  name: apmserver-sample
spec:
  version: "6.7.0"
  nodeCount: 1

  # optional "automagic" association with elasticsearch, would auto-populate some config fields:
  # - output.elasticsearch.hosts
  # - output.elasticsearch.username
  # - output.elasticsearch.password
  # TBD (we need some work on the cloud-k8s side here):
  # - output.elasticsearch.ssl.enabled
  # - output.elasticsearch.ssl.certificate_authorities
  elasticsearch:
    inCluster:
      name: <name of es resource>
      namespace: <namespace of es resource>

  # user-provided configuration:
  config:
    name: ${POD_NAME}

    apm-server:
      host: :8200 # blacklisted?
      secret_token: ${SECRET_TOKEN_FROM_KEYSTORE} # note: requires us to integrate with the apm server keystore, TBD
      ssl:
        enabled: false # probably want "true", and self-sign a cert by default, provide ability for customers to bring their own.
      #concurrent_requests: 1
      #max_unzipped_size: 5242880
      #read_timeout: 3600
      #rum:
      #  enabled: true
      #  rate_limit: 10
      #shutdown_timeout: 30s

    logging:
      json: true
      metrics.enabled: true

    output:
      elasticsearch:
        hosts:
          - https://elasticsearch-sample-es.default.svc.cluster.local:9200
        username: elastic-internal-apm-server
        password: ${ELASTICSEARCH_PASSWORD_FROM_KEYSTORE} # note: requires us to integrate with the apm server keystore, TBD
        ssl:
          certificate_authorities:
            - config/elasticsearch-certs/ca.pem
          enabled: true
        #max_bulk_size: 267
        #worker: 5
        #compression_level: 5
    #queue:
    #  mem:
    #    events: 2000
    #    flush:
    #      min_events: 267
    #      timeout: 1s
    #setup.template.settings.index:
    #  auto_expand_replicas: 0-2
    #  number_of_replicas: 1
    #  number_of_shards: 1
    #xpack.monitoring.enabled: true

  podTemplate:
    spec:
      containers:
      - name: apm-server
        resources:
          limits:
            memory: 1Gi
            cpu: 1000m
        volumeMounts:
        - name: elasticsearch-certs
          mountPath: /usr/share/apm-server/config/elasticsearch-certs
      volumes:
      - name: elasticsearch-certs
        secret:
          secretName: elasticsearch-certs

  http:
    service:
      metadata:
        annotations:
          service.beta.kubernetes.io/aws-load-balancer-connection-idle-timeout: "60"
      spec:
        # supports automatically creating a LoadBalancer for the HTTP endpoints.
        type: LoadBalancer
    # tls settings for APM server:
    tls:
      selfSignedCertificate:
        # subjectAlternativeNames allows providing a custom set of alternative names the certificate should contain.
        subjectAlternativeNames:
          - dns: foo.example.com
          - ip: 4.3.2.1