docs(integrations): move docs to ddtrace/contrib/internal/integration_name (#14068)

- Move integration docs to where the integration are defined. This
improves our package structure and helps avoid confusion around where
things are defined.
- Update integration contributing docs to match v3.0.0. The current docs
are out of date.

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Author: mabdinur

.github/CODEOWNERS

@@ -139,30 +139,19 @@ tests/profiling_v2                  @DataDog/profiling-python
 # MLObs
 ddtrace/llmobs/                                               @DataDog/ml-observability
 ddtrace/contrib/internal/openai                               @DataDog/ml-observability
-ddtrace/contrib/_openai.py                                    @DataDog/ml-observability
 ddtrace/contrib/internal/langchain                            @DataDog/ml-observability
-ddtrace/contrib/_langchain.py                                 @DataDog/ml-observability
 ddtrace/contrib/internal/botocore/services/bedrock.py         @DataDog/ml-observability
 ddtrace/contrib/internal/botocore/services/bedrock_agents.py  @DataDog/ml-observability
 ddtrace/contrib/botocore/services/bedrock.py                  @DataDog/ml-observability
 ddtrace/contrib/internal/anthropic                            @DataDog/ml-observability
-ddtrace/contrib/_anthropic.py                                 @DataDog/ml-observability
 ddtrace/contrib/internal/google_generativeai                  @DataDog/ml-observability
-ddtrace/contrib/_google_generativeai.py                       @DataDog/ml-observability
 ddtrace/contrib/internal/google_genai                         @DataDog/ml-observability
-ddtrace/contrib/_google_genai.py                              @DataDog/ml-observability
 ddtrace/contrib/internal/vertexai                             @DataDog/ml-observability
-ddtrace/contrib/_vertexai.py                                  @DataDog/ml-observability
 ddtrace/contrib/internal/langgraph                            @DataDog/ml-observability
-ddtrace/contrib/_langgraph.py                                 @DataDog/ml-observability
 ddtrace/contrib/internal/crewai                               @DataDog/ml-observability
-ddtrace/contrib/_crewai.py                                    @DataDog/ml-observability
 ddtrace/contrib/internal/openai_agents                        @DataDog/ml-observability
-ddtrace/contrib/_openai_agents.py                             @DataDog/ml-observability
 ddtrace/contrib/internal/litellm                              @DataDog/ml-observability
-ddtrace/contrib/_litellm.py                                   @DataDog/ml-observability
 ddtrace/contrib/internal/pydantic_ai                          @DataDog/ml-observability
-ddtrace/contrib/_pydantic_ai.py                               @DataDog/ml-observability
 tests/llmobs                                                  @DataDog/ml-observability
 tests/contrib/openai                                          @DataDog/ml-observability
 tests/contrib/langchain                                       @DataDog/ml-observability

ddtrace/contrib/_avro.py

@@ -393,6 +393,16 @@ integrations:
       min: 20.12.1
       max: 24.11.1
 
+- integration_name: gunicorn
+  is_external_package: true
+  is_tested: true
+  dependency_names:
+  - gunicorn
+  tested_versions_by_dependency:
+    gunicorn:
+      min: 20.0.4
+      max: 23.0.0
+
 - integration_name: google_genai
   is_external_package: true
   is_tested: true