Improve Security Filters Documentation

[asaikali]

Documentation at Security Filters leaves a lot of questions unanswered. Suggest that that section be enhanced by answering the following questions.

• In troubleshooting scenario how to get a list of what the filter chain looks like printed to the log?
• How to add a custom filter to the filter chain at a specific position?
• What are some use cases where a custom filter would be needed?
• Turn the list into a table that provides the name of the filter and a short description of what the filter does.
• Are all the filters always present even if a specified module is not being used? for example if my app is not using SAML is the Saml2WebSsoAuthenticationFilter still present in the filter chain?
• Is the filter chain listed in the docs configured by spring security or via spring boot auto configuration?

I believe answering the above questions in this section will make the docs much better.

[rwinch]

Thanks for the report @asaikali! Would you be interested in providing a PR?