[Add]: BuddyPress Site Health panel

[imath]

What needs to be done?

A new Markdown file should be added into the administration/tools subdirectory to explain how to access this panel and what the informations that are listed can be useful to debug / troubleshoot or submit a support request.

Handbook to add the page in

buddypress/docs/user

Tasks to accomplish

• [x] This task has been added to the "Todo" panel of the Documentation project.
• [ ] A PR has been submitted to the BuddyPress GH repository, it has been linked to this issue/task & the task was moved to the "In progress" panel of the Documentation project.
• [ ] Thecontributor/support/README.md was updated to contain a link to the page created by this task.
• [ ] The PR has been converted to a SVN patch and committed to the BuddyPress SVN repository & the task was moved to the "Done" panel of the Documentation project.

[imath]

Another task to accomplish once this page will be created is to update "markdown_source": "../contributor/support/README.md" so that it includes a link to the page created here. See #276