Removal of Test Cache and Redesign of Deployment Tests

[movchan74]

Summary:
This update removes the test cache from our testing infrastructure and introduces improvements to the deployment tests, simplifying and enhancing efficiency. The changes also include updates to the documentation to reflect these modifications.

Key Changes:

1. Test Cache Removal:

   • The test cache has been completely removed from the codebase and repository.
   • All tests have been updated to eliminate the usage of test cache.

2. Deployment Test Updates:

   • Redesigned deployment tests to be simpler and more efficient.
   • Deployment tests are automatically skipped if they require GPU and no GPU is available.
   • Replaced the Stable Diffusion deployment with a dummy deployment in test_haystack_component.py, which does not require a GPU.
   • Added environment variable SAVE_EXPECTED_OUTPUT to save the actual output as the expected output to simplify test creation.

3. Documentation Updates:

   • All references to the test cache were removed from the documentation.
   • Added instructions for creating new deployment tests.

Closes: #146, #80
Invalidates: #82, #50

[HRashidi]

LGTM 👍🏽