Add endpoint tag to legacy

[steveny91]

What does this PR do?

Add the a endpoint tag to the legacy version of the envoy check.

Motivation:

While going over the check, I notice that the OpenMetricsV2 implementation has a useful endpoint check. The legacy version however lacks this check. This can cause problems if a single agent were to monitor different stats_url endpoints. There might be no way to distinguish them from one another.

  envoy.server.state                                         gauge  1703021786  0                                                                  
  envoy.server.total_connections                             gauge  1703021786  0                                                                  
  envoy.server.uptime                                        gauge  1703021786  160                                                                
  envoy.server.version                                       gauge  1703021786  10011081    

to this:

envoy.server.state                                         gauge  1703087799  0                     endpoint:http://localhost:8001/stats         
envoy.server.total_connections                             gauge  1703087799  0                     endpoint:http://localhost:8001/stats         
envoy.server.uptime                                        gauge  1703087799  350                   endpoint:http://localhost:8001/stats         
envoy.server.version                                       gauge  1703087799  10011081              endpoint:http://localhost:8001/stats 

Additional changes:
Added papertrail comment in regards to one of the tests.

[github-actions]

Test Results

    6 files      6 suites   2m 20s ⏱️
  92 tests   90 ✔️   2 💤 0 ❌
279 runs  253 ✔️ 26 💤 0 ❌

Results for commit f346608.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (eb6538b) 90.53% compared to head (f346608) 90.63%.
Report is 8 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
confluent_platform	?
envoy	95.01% <100.00%> (+0.30%)	⬆️
hive	?
hivemq	?
hudi	?
ignite	?
jboss_wildfly	?
kafka	?
presto	?
solr	?
tomcat	?
weblogic	?

Flags with carried forward coverage won't be shown. Click here to find out more.

[Kyle-Neale]

LGTM