Adapt code based on kibana version constraints to use spec version

[jsoriano]

We are going to start relying on the spec version to determine the compatibility between packages and the stack, instead of using the kibana version as we do now.

We have to assess where the kibana version constraint is used and try to change to the new model instead.

Among other things, CI in the integrations repository should be revisited, to start Elatic stacks with packages that do not contain kibana.version in their manifests. Related code: https://github.com/elastic/integrations/blob/1a8a4b212b872bf46edbc8e5ab67af7ad5f76632/.ci/Jenkinsfile#L375-L389

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[jlind23]

@kpollich @jsoriano isn't this something we should pursue or did I miss something?

[jsoriano]

Yes, we should do this, this is planned for the current sprint. This is not so urgent because we don't have any package relying only on the spec version for its availability yet.