Add e2e/integration test & framework

[crandles]

Trickster has many unit tests, and integration-style tests per each package. However, after/in addition to unit tests, a comprehensive test should created for the whole codebase that leverages:

• actual running backend instances (e.g. prometheus, influx)
• an instance of trickster equivalent to main.go:main() (or as close as we can get)
  • Ideally, we should be able to switch between running an actual trickster instance (e.g. via container) or via calling the right Go code in a test

To do:

• Identify backends to include in test (will likely target a subset)
• Identify "user stories" that should be tested, per each backend

Goals:

• To test our actual implementation against real backends, and not just test our mock implementations
• To test our full stack with real clients
• Test should be executable from github action workflow, or locally
  • For local development, this should give us the ability to perform step-through debugging and better recreate reported issues
• To be able to perform race detection tests against the whole codebase

[crandles]

For the e2e side of this, running the build artifact could be paired with the following:

• avalanche - prometheus time series generator
• load test via k6
• (MAYBE) conformance test API via k6

going to focus on a single backend (prometheus) and defer full coverage.

[crandles]

For the near term we are settling on: k6 for load tests, docker + our test harness for integration tests.

#857
#926