[logs/ad] Support file tailing config from k8s pod annotation

[prognant]

What does this PR do?

Make #6883 slightly more generic by supporting annotation from both kubernetes (All runtime) & docker.

Motivation

Feature consistency.

Additional Notes

File path shall be relative to where the agent is running.
Add a slight modification to properly handle multiple logs config in kubernetes launcher, In that extend the following annotation will work :

• ad.datadoghq.com/logapp.logs: '[{"type":"file","path":"/tmp/share/test.log"}]', will collect log from /tmp/share/test.log and the container log if container_collect_all is set to true
• ad.datadoghq.com/logapp.logs: '[{"type":"file","path":"/tmp/share/test.log"},{"source":"my_source", "service":"my_service"}]', will collect log from /tmp/share/test.log and the container log with a custom source/service value
• ad.datadoghq.com/logapp.logs: '[{"type":"file","path":"/tmp/share/test.log"},{"source":"my_source", "service":"my_service", "type": "<CONTAINER_TYPE>"}]' (where <CONTAINER_TYPE> is the container runtime : cri-o, docker or containerd) will collect log from /tmp/share/test.log and the container log with a custom source/service value if type is set to the correct container runtime.

Note: source/service are set independently for each config.

Describe your test plan

Use the following pod annotation for testing.

apiVersion: v1
kind: Pod
metadata:
  name: logapp
  annotations:
    ad.datadoghq.com/logapp.logs: '[{"type":"file","path":"/tmp/share/test.log"}]'
spec:
  containers:
  - name: logapp
    image: mingrammer/flog:latest
    imagePullPolicy: Always
    command: ["/bin/flog"]
    args: ["-l", "-d", "2"]

Tests:

• Different container runtime with k8s
• Plain docker
• Assess that there are no side effects, especially regarding AD combination like ad.datadoghq.com/<container>.logs: '[{"type":"file","path":"/tmp/share/test.log"},{"source":"my_source", "service":"my_service"}]' leads to properly tagged log from the container and that the file tailer actually starts.

[ogaca-dd]

LGTM, just having a question.