upstream subset lb: add redundant keys support

[wbpcode]

Commit Message: upstream subset lb: add redundant keys support
Additional Description:

Description is same with the comment:

    // If true, redundant key/value pairs are allowed in the request (route, weighted cluster or dynamic)
    // metadata. By default, only when the request metadata has **same** keys with one of the subset
    // selectors and the values of related keys are matched, we will get valid subset. For example:
    //
    // .. code-block:: json
    //
    //   { "subset_selectors": [
    //       { "keys": [ "version" ] },
    //       { "keys": [ "stage", "version" ] }
    //   ]}
    //
    // A request with metadata ``{"redundant-key": "any", "stage": "prod", "version": "v1"}`` or
    // ``{"redundant-key": "any", "version": "v1"}`` can never get valid subset even if the values of
    // ``stage`` and ``version`` are matched because of the redundant key/value pair in the request
    // metadata.
    //
    // By set this to true, only the necessary key/value pairs will be evaluated and redundant key/value
    // pairs will be ignored. Take the above example, if the request metadata is ``{"redundant-key": "any",
    // "stage": "prod", "version": "v1"}``, the subset lb will keep the ``{"stage": "prod", "version": "v1"}``
    // as the request metadata for the evaluation. If the request metadata is ``{"redundant-key": "any",
    // "version": "v1"}``, the subset lb will keep the ``{"version": "v1"}`` as the request metadata for
    // the evaluation.
    //
    // .. note::
    //   To avoid the performance impact and potential complexity, subset lb will keep at much as possible
    //   key/value pairs in the request metadata. Take the above example, if the request metadata is
    //   ``{"redundant-key": "any", "stage": "prod", "version": "v1"}``, the subset lb will keep the
    //   ``{"stage": "prod", "version": "v1"}`` as the request metadata for the evaluation and will not
    //   try the ``{"version": "v1"}`` as the request metadata.

Risk Level: low. minor change.
Testing: unit.
Docs Changes: n/a.
Release Notes: added.
Platform Specific Features: n/a.

[repokitteh-read-only]

CC @envoyproxy/api-shepherds: Your approval is needed for changes made to (api/envoy/|docs/root/api-docs/).
envoyproxy/api-shepherds assignee is @adisuissa
CC @envoyproxy/api-watchers: FYI only for changes made to (api/envoy/|docs/root/api-docs/).

🐱

Caused by: #28874 was opened by wbpcode.

see: more, trace.

[adisuissa]

Thanks for working on this.
Left a high-level comment about this new feature.

[wbpcode]

/docs

[repokitteh-read-only]

Docs for this Pull Request will be rendered here:

https://storage.googleapis.com/envoy-pr/28874/docs/index.html

The docs are (re-)rendered each time the CI envoy-presubmit (precheck docs) job completes.

🐱

Caused by: a #28874 (comment) was created by @wbpcode.

see: more, trace.

[wbpcode]

This is more readable.

[wbpcode]

friendly ping @adisuissa

[wbpcode]

Re-assigned this to @zuercher because @zuercher is code owner of subset lb.

[wbpcode]

/docs

[repokitteh-read-only]

Docs for this Pull Request will be rendered here:

https://storage.googleapis.com/envoy-pr/28874/docs/index.html

The docs are (re-)rendered each time the CI envoy-presubmit (precheck docs) job completes.

🐱

Caused by: a #28874 (comment) was created by @wbpcode.

see: more, trace.

[wbpcode]

cc @zuercher test was updated. 😸

[wbpcode]

cc @adisuissa any other concern to the API? 🤔

[adisuissa]

Left a few nits, but otherwise api lgtm.
Consider emphasizing that this is a 2step algorithm, choosing the keys subset first, and only then matching their values (so it won’t be mistaken with choosing the subset of keys+values that match w/o the redundant keys)

[repokitteh-read-only]

🙀 Error while processing event:

evaluation error
error: context deadline exceeded

🐱

Caused by: #28874 was synchronize by wbpcode.

see: more, trace.

[wbpcode]

cc @adisuissa Thanks for your detailed review. Related comments are addressed and comment of API is updated.

[wbpcode]

Hi, @zuercher, could you give another LGTM. We updated API's comment after your code review. Thanks.

[wbpcode]

/assign-from @envoyproxy/envoy-maintainers

[repokitteh-read-only]

@envoyproxy/envoy-maintainers assignee is @zuercher

🐱

Caused by: a #28874 (comment) was created by @wbpcode.

see: more, trace.

[wbpcode]

cc @RyanTheOptimist (on-call maintainer) Hi, could you give this PR another LGTM?

@zuercher has approved this PR before. And after his approve, we just update the API's comments. But seems @zuercher is busy recently and has no github activities.

[wbpcode]

ho, @zuercher thanks 🙏