conformance tests for percentage-based request mirroring

[LiorLieberman]

What type of PR is this?
/kind test
/area conformance

What this PR does / why we need it:
Conformance tests for #3171 plus small updates to the GEP.
Tested with istio 1.24.1

Note: I also added a test case for fraction but it looks like it has an issue currently with the implementation I used (istio).

The specific test is failing, (which is good) so I think its in a good merge state. I also opened istio/istio#54357.

Mesh tests to follow

Which issue(s) this PR fixes:
Fixes #3171

Does this PR introduce a user-facing change?:

NONE

/cc @jakebennert @robscott

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: LiorLieberman
Once this PR has been reviewed and has the lgtm label, please assign danwinship for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[LiorLieberman]

/cc @jakebennert @robscott

[k8s-ci-robot]

@LiorLieberman: GitHub didn't allow me to request PR reviews from the following users: jakebennert.

Note that only kubernetes-sigs members and repo collaborators can review this PR, and authors cannot review their own PRs.

In response to this:

/cc @jakebennert @robscott

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[robscott]

Thanks @LiorLieberman! This is really well done

[robscott]

/cc @dprotaso

[LiorLieberman]

/cc @kflynn