[meta] Adding metrics support for logstash plugins

[purbon]

Meta issue to track progress while adding metrics support to logstash plugins:

Inputs

• logstash- input-beats
• logstash- input-couchdb_changes
• logstash- input-elasticsearch
• logstash- input-eventlog
• logstash- input-file
• logstash- input-gelf
• logstash- input-generator
• logstash- input-graphite
• logstash- input-heartbeat
• logstash- input-http (Add metrics for the http input logstash-plugins/logstash-input-http#58)
• logstash- input-http_poller
• logstash- input-jdbc (Add metrics to the jdbc input operations logstash-plugins/logstash-input-jdbc#155)
• logstash- input-kafka
• logstash- input-log4j
• logstash- input-lumberjack
• logstash- input-rabbitmq
• logstash- input-redis (Add metrics support for the redis input logstash-plugins/logstash-input-redis#48)
• logstash- input-s3
• logstash- input-sqs
• logstash- input-stdin
• logstash- input-syslog (Add metrics for syslog input logstash-plugins/logstash-input-syslog#28)
• logstash- input-tcp (Add metrics to tcp input logstash-plugins/logstash-input-tcp#56)
• logstash- input-twitter
• logstash- input-udp (Add metrics to udp input logstash-plugins/logstash-input-udp#24)

Filters

• logstash- filter-aggregate
• logstash- filter-anonymize
• logstash- filter-csv
• logstash- filter-date
• logstash- filter-dns
• logstash- filter-drop
• logstash- filter-fingerprint
• logstash- filter-geoip
• logstash- filter-grok
• logstash- filter-json
• logstash- filter-kv
• logstash- filter-metrics
• logstash- filter-multiline
• logstash- filter-mutate
• logstash- filter-ruby
• logstash- filter-sleep
• logstash- filter-split
• logstash- filter-syslog_pri
• logstash- filter-translate
• logstash- filter-urldecode
• logstash- filter-useragent
• logstash- filter-uuid
• logstash- filter-xml

Outputs

• logstash- output-csv
• logstash- output-elasticsearch
• logstash- output-elasticsearch_java
• logstash- output-email
• logstash- output-file
• logstash- output-graphite
• logstash- output-http
• logstash- output-kafka
• logstash- output-lumberjack
• logstash- output-rabbitmq
• logstash- output-redis
• logstash- output-s3
• logstash- output-stdout
• logstash- output-tcp
• logstash- output-udp

Codecs

• logstash- codec-avro
• logstash- codec-collectd
• logstash- codec-dots
• logstash- codec-es_bulk
• logstash- codec-fluent
• logstash- codec-graphite
• logstash- codec-json
• logstash- codec-json_lines
• logstash- codec-line
• logstash- codec-msgpack
• logstash- codec-multiline
• logstash- codec-plain
• logstash- codec-rubydebug

[purbon]

created this issue to track evolution of plugins metrics addition, so we know evolution of our efforts.