Support rendering tables of wiki front-matter

What does this MR do?

Adds <FrontMatterTable /> wiki tag. See #228538 (closed).

Examples of supported syntax:

<!-- Render a table of all front-matter of pages in the current wiki directory: -->
<FrontMatterTable />

<!-- Specify an absolute wiki directory: -->
<FrontMatterTable path="/Some-Folder" />

<!-- Specify a relative wiki directory: -->
<FrontMatterTable path=".." />

<!-- Restrict the table to only showing some front-matter columns: -->
<FrontMatterTable columns="some_key,some_other_key" />

<!-- Also show the full content of each wiki page: -->
<FrontMatterTable content />

<!-- Truncate the content of each wiki page to 80 characters: -->
<FrontMatterTable content-truncated=80 />

Screenshots

Create some wiki pages with front-matter like this:

Then create an index page with a tag like this:

And the index page will render a table like this:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• To test, first create the wiki pages with front-matter
  • (For now, you need to create the wiki pages with front-matter before enabling the :wiki_front_matter feature flag, due to #234899.)
• Then enable the feature flags:

bundle exec rails console
Feature.enable(:wiki_front_matter)
Feature.enable(:front_matter_table)

• Then create the index wiki page using the new tag

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

• Tested in all supported browsers

• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Closes #228538 (closed)

/cc @alexkalderimis, since you worked on !27706 (merged)