Switch to delta-preferred metrics temporality

[JonasKunz]

As discussed with other agent teams, we should switch to delta-preferred temporality.
This is a "potentially breaking change", but it can be reverted using configuration.

Also we should document somewhere that when using the vanilla otel agent, it is highly recommended to put it into delta-preferred temporality mode.

[SylvainJuge]

Do we have a "master issue" to coordinate efforts here ? As it spreads on many areas like docs, each per-platform elastic distribution, maybe the elastic otel collector, ... this could be relevant to keep track of all the moving pieces.

[JonasKunz]

No, good point. I think we should create one

[jackshirazi]

Isn't this it?