chore: expose search engine ping max time as a new environment variable

[jfcalvo]

Description

This PR will expose a new ARGILLA_SEARCH_ENGINE_PING_TIMEOUT environment variable allowing us to control the maximum time (in seconds) waiting for the search engine to be ready when starting up Argilla server.

The default value for this environment variable is still 60 seconds as before. I will modify our Argilla template on Hugging Face to set this to a higher value (120 for example).

This change is motivated by @davidberenstein1957 and @dvsrepo reporting errors on Hugging Face Spaces related with Argilla not starting up after waiting for Elasticsearch.

Task to do after merging this PR:

• [ ] Merge PR on Argilla template at HF Spaces setting a value of 120 seconds for this new environment variable: link to PR.

Refs #4946

Type of change

(Please delete options that are not relevant. Remember to title the PR according to the type of change)

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Refactor (change restructuring the codebase without changing functionality)
• [x] Improvement (change adding some improvement to an existing functionality)
• [ ] Documentation update

How Has This Been Tested

(Please describe the tests that you ran to verify your changes. And ideally, reference tests)

• [x] Manually testing the new environment variable locally.

Checklist

• [ ] I added relevant documentation
• [ ] follows the style guidelines of this project
• [ ] I did a self-review of my code
• [ ] I made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I filled out the contributor form (see text above)
• [x] I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)