LogstashAccessEncoder#fieldNames does not change the field name used by ContextJsonProvider #658
Description
Changing default field names on LogstashAccessEncoder by setting the fieldNames property does not change the name of the field used by the ContextJsonProvider.
The cause is the "instanceof" at line https://github.com/logstash/logstash-logback-encoder/blob/main/src/main/java/net/logstash/logback/composite/ContextJsonProvider.java#L57.
The "context" field is applicable to both IAccessEvent and ILoggingEvent and should therefore be declared in CommonLogstashFieldNames instead of LogstashFieldNames.