Cherry-pick #16455 to 7.x: [Metricbeat] Update Couchdb to v2

[sayden]

Cherry-pick of PR #16455 to 7.x branch. Original message:

What does this PR do?

Updates module to use a Strategy patern and decide between v1 and v2 Couchdb parsing. To do so, it has to do a pre HTTP request to root path / to know which version is deployed on each fetch (done in fetch to allow hot upgrades in container environment).

I have removed testdata tests because one of them was a bit unnecessary with our current testdata implementation (a timeout test which was testing testdata framework more than the module itself). The other testdata doesn't work anymore because more than one request is necessary now to check version.

Because we can only test in CI with a single version, I maintained current Dockerfile

Why is it important?

ATM, we were only parsing v1 metrics and v3 is going to be released soon. This PR introduces v2 parsing maintaining compatibility with our previous version.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
  - [ ] I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works

How to test this PR locally

• Launch v1 and v2 containers

docker run -d --name couchdb16 -p 15984:5984 couchdb:1.6
docker run -d --name couchdb23 -p 25984:5984 -p 25986:5986 couchdb:2.3

• Setup Metricbeat Couchdb module to point to both servers ./metricbeat modules enable couchdb and leave config similar to this:

- module: couchdb
  metricsets: ["server"]
  period: 10s
  hosts: ["localhost:15984", "localhost:25984/_node/_local/_stats", "localhost:25984/_node/nonode@nohost/_stats", "localhost:25986"]

• Check that events from v1 and v2 are being received in, for example, Kibana. You can see version in field service.version and the service.id must be the same for all paths of v2.
• Extra mile, check dashboards, they must maintain compatibility and show info of both servers.

Related issues

• Closes metricbeat couchdb module not working with couch 2.x #16352
• Relates CouchDB metribeat module #10354

Screenshots

I checked that dashboard still works.

[elasticmachine]

Pinging @elastic/integrations-services (Team:Services)