Add CI to validate challenge_config on PRs and master (fixes #98)

[NEHAJAKATE]

Fixes #98

Problem

EvalAI-Starters currently has no automated validation for challenge_config.yaml/challenge_config.yml on PRs or after merges to master.
This forces maintainers to manually verify changes post-merge, and invalid configs can slip into master.

What this PR adds

GitHub Actions workflow that runs on:

Pull requests targeting master (only when challenge_config.yaml|yml or related challenge packaging files change)

Pushes to master (same path filter)

Lightweight validator script github/ci_validate_challenge_config.py that:

checks YAML syntax

builds evaluation_script.zip

builds challenge_config.zip

optionally validates against the EvalAI API if secrets are provided (EVALAI_AUTH_TOKEN, EVALAI_HOST_TEAM_PK, EVALAI_HOST_URL)

Security / Safety note

This workflow runs on pull_request (not pull_request_target), so it does not receive repository secrets on PRs from forks, which keeps CI safe by default.
Optional EvalAI API validation is only meaningful when secrets are available (typically on trusted contexts like pushes to master or same-repo PRs, depending on repo settings).

Why this approach

Prevents “bad config merged → manual debugging later”

Provides fast feedback in PRs with minimal CI complexity

Avoids exposing secrets to untrusted PR code (GitHub default behavior for forks)

How to test (verified locally)
pip install -r github/requirements.txt
pip install pyyaml
python github/ci_validate_challenge_config.py
echo $?

Expected:

Exit code 0 for valid config

Exit code non-zero if YAML is invalid / packaging fails

[NEHAJAKATE]

Hi, just checking in to see if any additional changes or tests are needed from my side. Happy to update the PR accordingly. Thanks!