feat: Add information about relations to generated docs

[hermanschaaf]

This adds a Relations section to generated docs, with information about parent- and child relationships.

For example, a parent table might look like this:

## Relations
The following tables depend on `aws_accessanalyzer_analyzers`:
  - [`aws_accessanalyzer_analyzer_findings`](aws_accessanalyzer_analyzer_findings.md)
  - [`aws_accessanalyzer_analyzer_archive_rules`](aws_accessanalyzer_analyzer_archive_rules.md)

And a child table will look like this:

## Relations
This table depends on [`aws_accessanalyzer_analyzers`](aws_accessanalyzer_analyzers.md).

[erezrokah]

🚀