deprecate the builtin junitxml module and plan for moving it to a external plugin

[RonnyPfannschmidt]

followup to #1126

junitxml in pytest itself is broken and not seeing any real maintenance, as such it should be considered for removal from the core

• create a timeline
• create a external copy of the plugin that may replace/superseed the building plugin
• deprecate the builtin plugin
• remove the builting plugin

as the plugin is not part of the public api, it can be turned into a required dependency even in a minor release without needing to have a breaking release

it can however only turned into a optional thing by a major release

[nicoddemus]

Not sure I like the idea of the core depending on an external plugin, because the external plugin will also depend on pytest.

[rustyhowell]

I wouldn't mind taking a stab at updating and maintaining junitxml. I depend on this feature for work and am currently stuck on older Junit test report plugin in Jenkins because the newest one changes schema. I hastily submitted a merge request a few days ago, but it's clear that more thought has to be involved here. If we can come to a consensus on the direction of this feature, I am willing to do the work.

I see a couple of possible directions:

1. Make the breaking changes necessary and maintain compatibility with Jenkins Junit test plugin in the future (even if they change schema again).
2. Change this feature to be more generic (ie --xunitxml) and keep it as is, and create a new external plugin for Jenkins Junit parity.

[RonnyPfannschmidt]

@rustyhowell i'd like to coordinate this on the ml

i'd really like to get into a place where the junitxml plugin is aware of flavors and versions, and able to function in a context where pytest was executed logging serialized reports, and then using those reports to genrate the junitxml

[nicoddemus]

@rustyhowell has the new junit_family option been working for you?

[nicoddemus]

Closing this the plugin has seen both interest and maintenance in the last releases, so it seems it should stay on the core (for now).