feat(envoy-plugin): Add support to get response backend latency

[anurag-rajawat]

Description

This PR adds support to get response backend latency in envoy plugin.

Does this PR introduce a breaking change?

Checklist

• PR title follows the <type>: <description> convention.
• I use conventional commits in my commit messages.
• I have updated the documentation accordingly.
• I Keep It Small and Simple: The smaller the PR is, the easier it is to review and have it merged.
• I have performed a self-review of my code.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

Additional information for reviewer

Mention if this PR is part of any design or a continuation of previous PRs