Add Testing Framework with CI suite

[xuxey]

This PR adds a testing framework to write automated tests via Jest, per issue #14

Unit tests are defined in *.spec.ts files, and mocks can be injected within the beforeEach columns. Use attendees.service.spec.ts as a reference point to write future tests.

The CI suite runs the test suite for PRs and commits to main, as well as for branches starting with "test"

Side notes @rohannunu The sample tests are written on an outdated version of the schema. Please make sure to update these tests for the create function once this PR is merged in.

@aniketgargya since we're using the connection object directly for transactions, I've found a temporary workaround that injects a real connection to the dev mongo cluster.

[github-actions[bot]]

Coverage report

St.:grey_question:	Category	Percentage	Covered / Total
🟡	Statements	68.31% (+62.7% 🔼)	291/426
🔴	Branches	7.5% (+7.5% 🔼)	3/40
🔴	Functions	30.51% (+25.42% 🔼)	18/59
🟡	Lines	64.8% (+60.56% 🔼)	243/375

Test suite run success

12 tests passing in 10 suites.

Report generated by 🧪jest coverage report action from be30bfce07c0c55e591c3ab36a0a5b4218533a9b