feat(backend): snapshot test responses (#10039)

This pull request introduces a comprehensive backend testing guide and
adds new tests for analytics logging and various API endpoints, focusing
on snapshot testing. It also includes corresponding snapshot files for
these tests. Below are the most significant changes:

### Documentation Updates:
* Added a detailed `TESTING.md` file to the backend, providing a guide
for running tests, snapshot testing, writing API route tests, and best
practices. It includes examples for mocking, fixtures, and CI/CD
integration.

### Analytics Logging Tests:
* Implemented tests for logging raw metrics and analytics in
`analytics_test.py`, covering success scenarios, various input values,
invalid requests, and complex nested data. These tests utilize snapshot
testing for response validation.
* Added snapshot files for analytics logging tests, including responses
for success cases, various metric values, and complex analytics data.
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[[4]](diffhunk://#diff-63af007073db553d04988544af46930458a768544cabd08412265e0818320d11R1-R30)

### Snapshot Files for API Endpoints:
* Added snapshot files for various API endpoint tests, such as:
- Graph-related operations (`graphs_get_single_response`,
`graphs_get_all_response`, `blocks_get_all_response`).
[[1]](diffhunk://#diff-b25dba271606530cfa428c00073d7e016184a7bb22166148ab1726b3e113dda8R1-R29)
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- User-related operations (`auth_get_or_create_user_response`,
`auth_update_email_response`).
[[1]](diffhunk://#diff-49e65ab1eb6af4d0163a6c54ed10be621ce7336b2ab5d47d47679bfaefdb7059R1-R5)
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- Credit-related operations (`credits_get_balance_response`,
`credits_get_auto_top_up_response`, `credits_top_up_request_response`).
[[1]](diffhunk://#diff-189488f8da5be74d80ac3fb7f84f1039a408573184293e9ba2e321d535c57cddR1-R3)
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- Graph execution and deletion (`blocks_execute_response`,
`graphs_delete_response`).
[[1]](diffhunk://#diff-a2ade7d646ad85a2801e7ff39799a925a612548a1cdd0ed99b44dd870d1465b5R1-R12)
[[2]](diffhunk://#diff-c0d1cd0a8499ee175ce3007c3a87ba5f3235ce02d38ce837560b36a44fdc4a22R1-R3)##
Summary
- add pytest-snapshot to backend dev requirements
- snapshot server route response JSONs
- mention how to update stored snapshots

## Testing
- `poetry run format`
- `poetry run test` 

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  <!-- Put your test plan here: -->
  - [x] run poetry run test

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Nicholas Tindle <nicholas.tindle@agpt.co>

docs/content/platform/getting-started.md

@@ -342,6 +342,12 @@ To run the tests:
 poetry run test
 ```
 
+To update stored snapshots after intentional API changes:
+
+```sh
+pytest --snapshot-update
+```
+
 ## Project Outline
 
 The current project has the following main modules:

docs/mkdocs.yml

@@ -54,7 +54,9 @@ nav:
       - Frontend:
          - Readme: https://github.com/Significant-Gravitas/AutoGPT/blob/master/classic/frontend/README.md
 
-  - Contribute: contribute/index.md
+  - Contribute: 
+        - Introduction: contribute/index.md
+        - Testing: autogpt_platform/backend/TESTING.md
     
   # - Challenges:
   #     - Introduction: challenges/introduction.md