Convert metrics/collect task into a load-test-with-fortio task with support for POST APIs

[sriumcp]

Is your feature request related to a problem? Please describe the problem.
Fortio has numerous options for testing both GET and POST APIs. Currently, they are not available as part of metrics/collect task. In particular, testing POST APIs is not possible today with builtin metrics.

Describe the feature/solution you'd like

1. Rename versions to versionInfo in metrics/collect task.
2. Rename metrics/collect to load-test-with-fortio
3. Use Iter8 defined constants {{ PayloadFile }} and {{ FortioOutputFile }}
4. Support resolution of destinations with timeouts. Sometimes, this is checking readiness of routes (as opposed to readiness of kubernetes resources; they are different).
5. Enable the use of any fortio load testing command. For example:

- task: load-testing-with-fortio
  with:
    resolve:
      destinations: ["hello.default", "hello-candidate.default"] # do not start if you cannot resolve these paths
      timeoutSeconds: 20
    versionInfo:
    - script: | # test a POST API. A fortio file named `output.json` is expected as a side-effect of the script
        curl https://payload.com -o {{ PayloadFile }}
        fortio load -json {{ FortioOutputFile }} -grpc -ping -grpc-ping-delay 0.25s -payload-file {{ PayloadFile }} -c 2 -s 4 hello.default
    - script: | # re-use payload.json from earlier script
        fortio load -json  {{ FortioOutputFile }} -grpc -ping -grpc-ping-delay 0.25s -payload-file {{ PayloadFile }} -c 2 -s 4 hello.default

Will this feature/solution bring new benefits for Iter8 users? What are they?
Better load testing, including ability to test POST APIs.

Will this feature/solution bring new benefits for Iter8 developers? What are they?
Leverage Fortio documentation. Leverage Fortio features for testing POST APIs.

Does this issue require a design doc/discussion? If there is a link to the design document/discussions, please provide it below.
Yes. See above.

How will this feature be tested?

• Existing tests should pass.

How will this feature be documented?

• Change to metrics/collect task documentation.

[sriumcp]

Note: Please see #942

[sriumcp]

Related to #947