Store logs in /var/log

[zrhoffman]

This PR

• changes configuration to log Traffic Router to /var/log/traffic_router instead of /opt/traffic_router/var/log
• changes configuration to log Traffic Monitor to /var/log/traffic_monitor instead of /opt/traffic_monitor/var/log

• changes configuration to log Traffic Stats to /var/log/traffic_stats instead of /opt/traffic_stats/var/log

  so that the logs are on a different partition than the application itself.

---

## Which Traffic Control components are affected by this PR?

• Documentation
• Traffic Monitor
• Traffic Router
• Traffic Stats
• CDN in a Box
• Automation - Ansible roles
• unknown

What is the best way to verify this PR?

If this is a bugfix, which Traffic Control versions contained the bug?

PR submission checklist

• [x] This PR has tests
• [x] This PR has documentation
• [x] This PR has a CHANGELOG.md entry
• [x] This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 65.77%. Comparing base (26a2f6a) to head (900cf16). Report is 6 commits behind head on master.

:exclamation: Current head 900cf16 differs from pull request most recent head 72834a2. Consider uploading reports for the commit 72834a2 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #7979 +/- ## ========================================= Coverage 65.77% 65.77% Complexity 98 98 ========================================= Files 327 327 Lines 13010 13010 Branches 998 998 ========================================= Hits 8557 8557 Misses 4091 4091 Partials 362 362 ``` | [Flag](https://app.codecov.io/gh/apache/trafficcontrol/pull/7979/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache) | Coverage Δ | | |---|---|---| | [traffic_router_unit](https://app.codecov.io/gh/apache/trafficcontrol/pull/7979/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache) | `29.03% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache#carryforward-flags-in-the-pull-request-comment) to find out more.

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[ntheanh201]

+1 this idea, it would be better for the logs agent's permissions

[zrhoffman]

After running Dev CIAB on the PR code, couldn't find the log files either at /opt/traffic_router/var or /var/log/.

The TR logs show up for me in /var/log/traffic_router.

[root@trafficrouter traffic_router]# ls -l
total 76
-rw-r--r-- 1 root root     0 Apr 10 18:52 access.log
-rw-r--r-- 1 root root 73560 Apr 10 18:55 traffic_router.log
[root@trafficrouter traffic_router]# tail -f access.log

They also show up for docker-compose logs -f trafficrouter.

Also couldn't find the log file in TM container as well.

The TM logs are printed to stdout only with no files

https://github.com/apache/trafficcontrol/blob/900cf169757b007e106ecdf112f9c520fbdd7635/infrastructure/cdn-in-a-box/traffic_monitor/traffic_monitor.cfg#L8-L13

https://github.com/apache/trafficcontrol/blob/900cf169757b007e106ecdf112f9c520fbdd7635/infrastructure/cdn-in-a-box/variables.env#L76-L81