Add ORT header rewrite check tool

[rob05c]

Adds a helper utility for checking that all remap.config header
rewrite directives have a matching file.

The header rewrite directive and file generation has a lot of conditions, so it's difficult to ensure they match identically. This provides users and developers a tool for checking code and data generate matching directives and files correctly.

Includes documentation in the tool directory.
No tests, is a standalone tool that doesn't affect production code paths.
Includes changelog.

• This PR is not related to any other Issue

Which Traffic Control components are affected by this PR?

Tool is useful to ORT, but does not affect ORT or any other production code path.

What is the best way to verify this PR?

See readme, run tool according to instructions.

If this is a bug fix, what versions of Traffic Control are affected?

Not a bug fix.

The following criteria are ALL met by this PR

• This PR includes tests OR I have explained why tests are unnecessary
• This PR includes documentation OR I have explained why documentation is unnecessary
• This PR includes an update to CHANGELOG.md OR such an update is not necessary
• This PR includes any and all required license headers
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

Additional Information

[rob05c]

https://github.com/apache/trafficcontrol/tree/master/traffic_ops_ort/plugin_verifier is capable of this