Polish MultipartConfigElement support

Polish MultipartConfigElement changes introduced in commit e8e59ea6
as follows:

- Fix javadoc formatting
- Fix tab/spaces formatting
- Fix asciidoc formatting
- Move creation of MultipartConfigElement into MultipartProperties
- Add @Since tags
- Restore random port in tests
Polish
Polish couchbase support

Polish couchbase support to:
- Extract properties into its own class
- Remove unnecessary inner configuration class
- Add since tags
- Format code and add `this.` references
Polish mongo changes

Restore formatting and fixup doc comments.
Rename MongoTemplateAutoConfiguration

Rename MongoTemplateAutoConfiguration to MongoDataAutoConfiguration
since it now configures more than just the template.