Feed sync

[syspect-sec]

What

The comprehensive guide to new and legacy feed sync tools is now available.

Why

Provide users with a comprehensive guide to Greenbone feed sync tooling

Checklist

• entry added to changelog.md
• most recent changes to greenbone/docs main branch have been merged

[syspect-sec]

Although the auto merge fails (Build the Greenbone Documentation / Build Documentation (pull_request) ) due to during the auto build, myst reports an error: /home/runner/work/docs/docs/src/feed-sync.md:37: WARNING: 'myst' cross-reference target not found: 'available-feed-types' [myst.xref_missing], the upon second compile, the docs build fine and even after the first, build, (and second) the link is active and works to redirect to the correct location.

Interestingly, although the Greenbone docs use the same syntax for inline, same page links in other places, I cannot find any reference for using the [link-text](#header-title) method on either the commonmark.org markdown tutorial, or the recommended syntax guide. Although, the [link-text](#header-title) method seems to use the standard HTML internal linking syntax to headers by name, so I guess that's why it works even though it's not officially supported?

Also, I have tracked down the issue to seems to be all fourth level header links, and I've opened an issue on the MySTParser GitHub page.

[cfi-gb]

Note that the deprecated / old greenbone-nvt-sync has been now removed completely in the scanner with / since greenbone/openvas-scanner#1589 so some adjustments to this PR might be required.