[feat gw-api]support multiple header value in condition

[shuqz]

Description

route match headers does not allow multiple http header values for same header name, but ALB supports it. we now allow customer to parsing string with comma so we can separate values by comma. customer can also choose to escape it if needs to be literal.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested

      matches:
        - headers:
            - name: "version"
              type: Exact
              value: "bar\\,bat"
            - name: "headerOne"
              type: Exact
              value: "value1,value2"

gives

• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[shraddhabang]

/lgtm
/approved

[zac-nixon]

/lgtm
/approved

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: shuqz, zac-nixon

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

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [zac-nixon]

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