lua: add new function to get the name of the matched route

[agrawroh]

Description

This PR adds a new function called routeName() to LUA through the Stream Info API. This allows Lua scripts to determine which route was matched for the current request.

Fixes: #35426

Example Usage

function envoy_on_request(request_handle)
  local route_name = request_handle:streamInfo():routeName()
  request_handle:logInfo("Request matched route: " .. route_name)
end

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Commit Message: lua: add new function to get the name of the matched route
Additional Description:
Risk Level: Low
Testing: Added Unit Tests
Docs Changes: Added
Release Notes: Added