Simplify interactions with GeoStore

[mbarto]

Description

If we have this: https://github.com/geosolutions-it/geostore/issues/206 We can remove all the convoluted logic needed to load / save complex resources, replacing them with a single API call.

What kind of improvement you want to add? (check one with "x", remove the others)

• [ ] Minor changes to existing features
• [ ] Code style update (formatting, local variables)
• [x] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Other... Please describe:

Other useful information