PaaS-friendly metrics (#4874)

* prom-client JSON to InfluxDB line protocol converter

* Converts a metric with separate names

* prom-client JSON to InfluxDB line protocol (version 2) converter

* Server has instance id

* Read the instance id from an environment variable

* More unit tests for instance-metadata

* Log instance id

* Push influx metrics

* INSTANCE_ID with dyno metadata

* Prepare influx metrics in one place

* Influx metrics endpoint should return metrics

* More readable tests

* Env added to instance metadata

* hostname as an instance label value

* HEROKU_DYNO_ID as an instance id for heroku

* Instance env can be set by env variable

* HEROKU_APP_NAME as an instance env

* Log instance metadata as a JSON

* Typo fix

* Code refactoring in tests

* wait-for-expect dev dependency added

* Test for pushing metrics

* Test for pushing metrics

* Use basic authentication for pushing metrics

* intervalSeconds=2 for development env

* Using existing methods

* TODOs removed

* Schema for influx credentials

* Influx config removed from config files

* Require username and password when influx metrics are enabled

* Unused args removed

* pushing component should log errors

* Speed up tests

* should log error responses

* InstanceMetadata class replaces by simple object

* Influx metrics can be configuredd by env variables

* Use application label name instead of service

* Unused code removed

* Integration test for prom-client and converter

* metrics.influx.enabled configuration option added

* Improved influx configuration schema

* instanceMetadata validation

* Typo fix

* Default value for env

* metrics.infux.hostnameAsAInstanceId added

* should add hostname as an instance label when hostnameAsAInstanceId is enabled

* Default values for influx configuration

* flatMap is not available in Node.js 9.4

* Env vars removed from Procfile

* Better instance metadata values in tests

* Typo fix

* lodash.groupby added to prod dependencies

* Allow other keys in private config

* Missing test - should allow other private keys when influx metrics are enabled

* Missing test - should require private metrics config when influx configuration is enabled

* log.error instead of console.log

* metrics.influx.uri -> metrics.influx.url

* Unused arguments removed

* async removed

* promisify sendMetrics

* Allow to disable prometheus metrics

* Create test server with custom config

* 'metrics-influx' resource removed

* 'metrics-influx' resource removed

* Private config schema flattened out

* Extra code removed in Prometheus tests

* promisify moved outside of the class

* Do not throw errors from got in a specific test

* hostnameAliases added

* instanceIdFrom added

* instanceIdEnvVarName added

* envLabel added to schema

* instanceMetadata is not used by InfluxMetrics

* Instance metadata removed

* hostnameAsAnInstanceId removed

* A comment added

* waitForExpect removed

* Unused code removed