enhancement: add option to skip acyclic check

[CodeMonkeyF5]

Support skip of acyclic check for cases where cyclical includes are warranted.

Proposed changes

If the file parsed is not the root conf file, then no need to perform acyclic check. If no root conf file is specified for the parsing options, then perform the acyclic check.

This allows for separate parsing of multiple configuration files without getting a "configs contain include cycle" error for ones that are not the root conf.

Issue: https://github.com/nginxinc/nginx-go-crossplane/issues/81

Checklist

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• [x] I have read the CONTRIBUTING document
• [x] If applicable, I have added tests that prove my fix is effective or that my feature works
• [x] If applicable, I have checked that any relevant tests pass after adding my changes
• [x] I have updated any relevant documentation (README.md)