Adding generic_logs template for hints autodiscovery

[gizas]

NOT TO MERGE UNTIL #2986 is merged

• Enhancement

What does this PR do?

This PR adds the generic_logs template that needs to be used in an Elastic Agent Standalone scenario in order to support by default the container log processing.

This PR is the continuation of #2386 (comment) in order to add the missing template needed to support the default behaviour of collection of logs

Why is it important?

It is important in order to allow log collection for k8s pods for the hints aytodiscovery scenario
Relevant documentation PR is added here: https://github.com/elastic/ingest-docs/pull/304/files

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

How to test this PR locally

1. Install a local kubernetes cluster with kind
2. Create your stack elastic-package stack up -d -vvv --version=8.8.1
3. Download and install the elastic-agent-standalone manifest with the changes described in the documentation PR

Enabling hints in the kubernetes standalone manifest:

providers.kubernetes:
  node: ${NODE_NAME}
  scope: node
  hints:
    enabled: true
    default_container_logs: false 

Example to manually mount the needed generic_logs template under the inputs.d folder of Elastic Agent

volumeMounts:
- name: external-inputs
  mountPath: /etc/elastic-agent/inputs.d/generic_logs.yml
...
volumes:
- name: external-inputs
  hostPath:
    path: /var/log/test/generic_logs.yml

4. Install agent manifest
5. Install nginx manifest

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: nginx
  name: nginx
  namespace: default
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
      annotations:
        co.elastic.hints/package: "generic_logs.container_logs"
        co.elastic.hints/stream: "stderr"
    spec:
      containers:
      - image: nginx
        name: nginx

5. Inspect the rendered configuration inside Elastic Agent

/usr/share/elastic-agent# /elastic-agent inspect -v --variables --variables-wait 2s

6. Exec to nginx code and produce stdout and stderror outputs:

kubectl exec -ti nginx-654557c679-rzrtt -- bash
root@nginx-654557c679-rzrtt:/# echo "stdout message" >> /proc/1/fd/1
root@nginx-654557c679-rzrtt:/# echo "stderror message" >> /proc/1/fd/2

7. Login to kibana and observe the stderror stream
   

[mergify]

This pull request does not have a backport label. Could you fix it @gizas? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 8./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2023-07-05T12:27:42.142+0000

• Duration: 26 min 30 sec

Test stats 🧪

Test	Results
Failed	0
Passed	5951
Skipped	23
Total	5974

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

Expand to view the GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• /package : Generate the packages.

• run integration tests : Run the Elastic Agent Integration tests.

• run end-to-end tests : Generate the packages and run the E2E Tests.

• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	98.684% (75/76)	👍
Files	68.582% (179/261)	👍
Classes	67.146% (327/487)	👍
Methods	54.136% (1034/1910)	👍
Lines	40.293% (11861/29437)	👎 -0.061
Conditionals	100.0% (0/0)	💚

[ChrsMark]

This generic_logs.container_logs in co.elastic.hints/package: "generic_logs.container_logs" bugs me tbh.
What do you think about skipping the generic_logs. prefix completely? This means we would need ofc to change the implementation at https://github.com/ChrsMark/elastic-agent/blob/cdd839de32c75b40b1ac142e371cf6bb6da0e9a6/internal/pkg/composable/providers/kubernetes/pod.go#L403.