Test to ensure website checks/filters are in alphabetical order at summary pages

[romani]

continuation of #14840 that was for navigation left panel
See update https://github.com/checkstyle/checkstyle/pull/15995/files

In addition, we need ordering at summary/index pages of
Example:
https://checkstyle.org/filters/index.html
https://checkstyle.org/checks.html
https://checkstyle.org/checks/annotation/index.html
https://checkstyle.org/filefilters/index.html

[mohitsatr]

on it