add wildfly.yaml to JMX scraper

[SylvainJuge]

Description:

• add wildfly support for jmx scraper with dedicated YAML configuration
• adds wildfly tests using jboss-client.jar for using HTTP management API
• fixes support for login/pwd authentication
• adds a test webapp needed to test wildfly session metrics
• moves existing test app to dedicated module for simplicity (and making it similar to test webapp)
• fixes use of plural form in units in wildfly.groovy to fit the stable convention for metric units.

Part of #1362

Notes:

In the original groovy implementation session metrics are not tested, this requires deploying and application to the container, this is not properly tested in the YAML implementation.

In the original groovy implementation the gatherer was run directly from the same docker container probably for simplicity as jboss-client.jar is directly available.
When using two containers, the jar needs to be copied from wildfly container to scraper container and it complicates authentication: login/pwd can be skipped if both processes run on the same host and can access the same filesystem.
Testing here is done using two distinct containers as this setup is a bit more complex and thus likely to fail (doing so here helped me find that we did not handle it properly).