Migrate molotov-based load tests to Locust

[Data Sync User]

The load tests for Contile currently use Molotov. I suggest we migrate them to use locust, since that has been working well for Merino.

Resources

• https://github.com/mozilla-services/contile-loadtests
• https://github.com/mozilla-services/merino-py/tree/main/tests/load

Acceptance Criteria

• Load tests cover Firefox user (status code 200) and Non-Firefox user (status code 403) requests to the /v1/tiles endpoint
• Load tests follow precedent for easy Continuous Delivery integration
• Load tests have Docker support
• Load tests have Kubernetes support
• README documentation includes:
  • Contribution guidelines
  • Local and distributed execution instructions

┆Issue is synchronized with this Jira Task
┆Epic: Implement Continuous Deployment for Contile