[otel] Add e2e test for httpjson input and integration test refactoring

[khushijain21]

What does this PR do?

This PR is part of supporting non-metric input types in otel mode. It adds e2e test for httpjson input. It also refactors/deletes integration tests with duplicated functionality.

Why is it important?

To support non-metric input types

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

Disruptive User Impact

How to test this PR locally

source ./env.sh; AGENT_VERSION=9.1.0 go test -tags integration -run TestOtelFilestreamInput ./testing/integration -count=1 -v

Related issues

• Part of https://github.com/elastic/ingest-dev/issues/4872

[mergify]

This pull request does not have a backport label. Could you fix it @khushijain21? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-./d./d is the label that automatically backports to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[khushijain21]

hybrid functionality and document equivalency is covered by TestOtelFilestreamInput test

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarQube

[elasticmachine]

💔 Build Failed

• Buildkite Build
• Commit: 63d6306

Failed CI Steps

• Win2022:non-sudo:default
• Win2022:non-sudo:default
• Win2025:non-sudo:default
• Win2025:non-sudo:default

History

• 💔 Build #21080 failed 4354ec1
• 💔 Build #21066 failed dc160c0
• 💔 Build #20998 failed 652ecbd

cc @khushijain21

[elasticmachine]

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