feat: introduce RegexClassifier for classifying errors via cfg

[agavra]

Description

This change introduces the ability to use config to classify errors as one of UNKNOWN, USER or SYSTEM (see #5374 for more information) via regex patterns.

Testing done

Tested with:

ksql.error.classifier.regex.1=USER .*task directory .* doesn't exist and couldn't be created.* 

And saw the following in the logs:

[2020-05-19 10:48:46,336] ERROR Unhandled exception caught in streams thread _confluent-ksql-default_query_CTAS_COUNTS_0-49406875-bc65-4fe2-9932-640c88dac8ae-StreamThread-3. (io.confluent.ksql.engine.KsqlEngine:43)
org.apache.kafka.streams.errors.ProcessorStateException: task directory [/tmp/kafka-streams/_confluent-ksql-default_query_CTAS_COUNTS_0/1_0] doesn't exist and couldn't be created
...
[2020-05-19 10:48:46,968] WARN Classified error for queryId _confluent-ksql-default_query_CTAS_COUNTS_0 under regex pattern .*task directory .* doesn't exist and couldn't be created.* as type USER. (io.confluent.ksql.query.RegexClassifier:71)

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[rodesai]

LGTM!