rename SylvaUnitsReleaseTemplate into SylvaUnitsReleasePreset

a posteriori summary

There is a convergence of view for renaming SylvaUnitsReleaseTemplate into SylvaUnitsReleasePreset.

discussion

We've realized in the past months/weeks that the "template" word in SylvaUnitsReleaseTemplate is not the best one:

• the origin idea was that it plays for SylvaWorkloadCluster a role similar as a resource template in the k8s ecosystem (e.g. a pod template in a Deployment spec)
• ... but even initially this wasn't very relevant, since the SylvaUnitsReleaseTemplate would never have to be a complete SylvaUnitsRelease spec
• ... and "template" carry the idea of "something based on which we create multiple things based on the same ", which isn't really relevant here either, because the SylvaUnitsReleases derived from a given SylvaUnitsReleaseTemplate may all be very different in the end
• ... and "template" in Sylva context collides with Helm "templates" (golang text template) like in templating engine
• ... and "template" is also used in the context of Kunai, where it was adopted to designate the text template (Kunai uses Handlebars.js library)

... so we should think about a better name, and the earlier is the better!

Candidates (with my own comments/pros/cons)

• "template"
• "element"
  • carries the idea, but collides with sylva-elements
• "bit"
  • a bit too informal to my taste
• "fragment"
  • I personally like it a lot
  • a tiny bit too long -> "frag"
• "stub"
  • does not carry the idea that well, I find, but might work
• "proto"
• "slice"
• "preset" (proposed by @stoub)