Init load tests

[ZoranPandovski]

Description

This PR:

1. Adds initial load tests and tests for PostgreSQL Integration (NOTE: this is not connected to the GitHub Actions for now)
2. Runs unit tests for handlers using coveralls
3. Add README for tests
4. Exclude some of the outdated hackhathon assets

Fixes #issue_number

Type of change

(Please delete options that are not relevant)

• 🐛 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 not to work as expected)
• 📄 This change requires a documentation update

Checklist:

• My code follows the style guidelines(PEP 8) of MindsDB.
• I have appropriately commented on my code, especially in complex areas.
• Necessary documentation updates are either made or tracked in issues.
• Relevant unit and integration tests are updated or added.

[ZoranPandovski]

@MinuraPunchihewa Please review now 🙌

[MinuraPunchihewa]

@ZoranPandovski Just left a couple more minor comments.

[MinuraPunchihewa]

@ZoranPandovski It looks like the added tests are failing, but I came across this,
https://stackoverflow.com/questions/65692711/using-python-coveralls-from-github-actions-returns-could-not-submit-coverage-4

I am guessing this might solve our problem?

[ZoranPandovski]

@MinuraPunchihewa I think this is ready