[Feature][Helm] Enable sidecar configuration in Helm chart

[kevin85421]

Why are these changes needed?

This PR exposed an interface in KubeRay helm charts to enable users to configure sidecar containers (See the logging documentation and #353 for more details).

Explanation of the interface:

.Values.fluentBitConfigMaps

fluentBitConfigMaps:
  - name: fluentbit-config
    fluentBitConf: |
      [INPUT]
          Name tail
          Path /tmp/ray/session_latest/logs/*
          Tag ray
          Path_Key true
          Refresh_Interval 5
      [OUTPUT]
          Name stdout
          Match *

• .Values.fluentBitConfigMaps[0].name: Name of the ConfigMap.
• .Values.fluentBitConfigMaps[0].fluentBitConf: Used to configure fluentBit. Note that this configuration assumes logs are mounted on /tmp/ray.

.Values.{head, worker, additionalWorkerGroups.smallGroup}.fluentBitConfigMap

fluentBitConfigMap:
  enabled: true
  logVolumeMount:
    mountPath: /tmp/ray
    name: log-volume
  configMapName: fluentbit-config

• enabled: Whether enable sidecar feature on the head, worker, and smallGroup pods. This configuration is optional, and the default value is false.
• logVolumeMount.mountPath: The mount path of the log volume should be synchronized with .Values.fluentBitConfigMaps.fluentBitConf
• logVolumeMount.name: This field should be synchronized with .Values.{head, worker, additionalWorkerGroups.smallGroup}.volumes.
• configMapName: The config map name should exist in .Values.fluentBitConfigMaps.

Related issue number

Closes #511

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(

[DmitriGekhtman]

Sorry, I was a bit unclear in the issue description --

I was suggesting adding support for arbitrary lists of sidecar containers, as in
https://github.com/helm/charts/blob/master/stable/prometheus/values.yaml#L565
https://github.com/helm/charts/blob/master/stable/prometheus/templates/deployments/server.yaml#L149-L151

This would enable users to specify sidecar containers for log processing using any tool (not just fluentbit).
There are other uses for sidecar containers too (e.g. custom networking setups).