Enable checkstyle on autoconfigure/docs modules

[therepanic]

The motivation to do this came from @onobc's comment at #223 (comment). I think it would be worthwhile for us to include checkstyle at least in the autoconfigure module.

There were classes such as GrpcSecurityAutoConfiguration and OAuth2ResourceServerAutoConfiguration that contained non-static classes, which should not be done. In this case, I split them into new classes so that checkstyle would pass.

Also, the GrpcClientAutoConfigurationTests test is currently failing. I would like to ask if anyone has any ideas as to why this is happening.

[dsyer]

It seems to be this that causes the build failure. I don't see why this should be a blocker.

[onobc]

I think we can get this in after the release.

[onobc]

Thank you for tackling this one @therepanic . I have left a couple of comments that should account for the test failures. That being said, I need more time to digest the large changes in the auto-configuations (I always am extra careful w/ these changes as they can wreck havoc on things in a very subtle way).

Can you describe why the checkstyle required such large refactoring in this area? Also, remember that if we want to make checkstyle ignore sections we can do ...

//CHECKSTYLE:OFF
var myBlockOfCodeThatIDontWantToDealWithRightNow = true;
....
//CHECKSTYLE:ON

Once we get this to a happy state I think we should wait to merge this until after the 0.9.0 release. @dsyer wdyt?

[therepanic]

Thank you for your review. As you can see, most of the changes were made to the order of imports, the order of methods, and so on. Also, the order in javadoc. All of this accumulated over time, which is why so many changes had to be made.

I force-pushed because I accidentally touched pom.xml in the test module, which is not related to these changes. I also added a commit that fixes your comment. However, that test still fails.

[therepanic]

I had to do a rebase because after all the fixes, the code still failing due to f90cecc.

In the last commit, I made all the corrections. I also disabled (at least temporarily) checkstyle on the doc module. I looked at what corrections needed to be made for checkstyle to approve the doc module and changed my mind. In order for checkstyle to pass in the doc module, we need to write an empty constructor in ConfigurationPropertiesAsciidocGenerator and replace all System.out.

What do you think about this? It seems to me that this is the very class for which we do not need to have an empty constructor. In any case, if we do checkstyle, we will also have to replace System.out with logging in another way.

[onobc]

Changes look good to me. Thank you for tackling this @therepanic !