feature: add checkstyle config

...main/java/de/fitko/fitconnect/api/config/Environment.java

...ain/java/de/fitko/fitconnect/api/config/SenderConfig.java

...java/de/fitko/fitconnect/api/config/SubscriberConfig.java

.../fitko/fitconnect/api/domain/model/metadata/Metadata.java

...fitconnect/api/domain/model/metadata/SignatureFormat.java

.../domain/model/metadata/attachment/AttachmentWithData.java

...connect/api/domain/model/submission/CreateSubmission.java

...o/fitconnect/api/domain/model/submission/ServiceType.java

...ko/fitconnect/api/domain/validation/ValidationResult.java

...rc/main/java/de/fitko/fitconnect/api/services/Sender.java

...ain/java/de/fitko/fitconnect/api/services/Subscriber.java

...e/fitko/fitconnect/api/services/crypto/CryptoService.java

.../fitconnect/api/services/crypto/MessageDigestService.java

...fitko/fitconnect/api/services/events/EventLogService.java

.../fitconnect/api/services/events/SecurityEventService.java

...fitconnect/api/services/submission/SubmissionService.java

...fitconnect/api/services/validation/ValidationService.java

checkstyle-suppressions.xml

checkstyle.xml

client/pom.xml