docs: add the print page

[kkedziak-splunk]

Issue number: ADDON-75611

Summary

Changes

Please provide a summary of what's being changed

Documentation changes: added print button that shows the whole documentation on one page.

In order to enable this feature, first level headings needed to be added to files.

User experience

Please describe what the user experience looks like before and after this change

None

Checklist

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• [x] I have performed a self-review of this change
• [ ] Changes have been tested
• [ ] Changes are documented
• [x] PR title follows conventional commit semantics

[kkedziak-splunk]

For some reason the modular_input section does not appear in the pring page's TOC.

Resulting also in a numeration issue: