Add support for bat-core

[mrzarquon]

bat-core is a bash testing framework that we should do more work around:

https://bats-core.readthedocs.io/en/stable/index.html

It allows for us to test that snyk-bulk is detecting the right number of projects at a minimum for each languages entrypoint.

MVP:

• For each language, test that running a snyk bulk --test --test-count returns a predetermined number of tests
• Each language will have it's own series of a tests in tests/{language}
• Keeping with our test matrix practice, we will then add a single job that will run a bats tests against name: Test ${{ matrix.language }}

Other notes

• Long term we should plan on a smarter smoke test (ie, if only entrypoints/python.sh is modified, just run a python language job, but if cmdline.sh or util.sh - the common libraries - then run all languages)
• a 'release' job will require all the matrix tests having to pass before tagging a release