[9.3] (backport #12854) Default inputs using dynamic providers to the process runtime

[mergify]

What does this PR do?

Default inputs using dynamic providers to the process runtime.

I've also refactored the runtime override tests for this feature a bit.

Why is it important?

The otel runtime isn't efficient at reloading configuration right now. Nonetheless, we want to enable it by default for inputs which are often used in highly dynamic environments, like filestream in Kubernetes. This change allows us to do that without impacting those use cases.

Checklist

• I have read and understood the pull request guidelines of this project.
• 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

Build agent and try running an input with a local dynamic provider:

inputs:
- id: "${local_dynamic.id}"
  type: filestream
  prospector.scanner.fingerprint.enabled: false
  file_identity.native: ~
  use_output: default
  paths: [...]

outputs:
  default:
    type: elasticsearch
    hosts: [http://localhost:9200]
    username: elastic
    password: elastic
agent:
  monitoring:
    enabled: false
  internal.runtime.filebeat.filestream: otel
  internal.runtime.dynamic_inputs: process
agent.logging.level: debug
providers:
  local_dynamic:
    items:
    - vars:
        id: filestream-1

Filestream should run in the process runtime.

Related issues

• Closes [beats receivers] Default inputs using dynamic providers to the process runtime by default #12750

---

This is an automatic backport of pull request #12854 done by [Mergify](https://mergify.com).

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[swiatekm]

This should wait until after 9.3.1 release.

[ebeahan]

Holding off on merging until after 9.3.1

[mergify]

This pull request has not been merged yet. Could you please review and merge it @swiatekm? 🙏