"Content update comments" action: list changes in navigation files (aka taxonomy on the left of the page)

[tbouffard]

DISCLAIMER: should be done after #766 is implemented to ease the maintenance

In #534, we fix the list of "updated pages" to not display a wrong link due to change in a navbar, but changes in the navbar files are still not listed.

We could create a new list that mention them to state to the reviewer they should check the left navigation part.

Notice that could also be done for:

• usage of partials (such files are AsciiDoc files https://docs.antora.org/antora/latest/page/partials/)
• if we put AsciiDoc files in other directories (https://docs.antora.org/antora/latest/standard-directories/). Supported by feat: Support link generation for page declare in submodule #751