Migrate GeoStore and Http-Proxy into MapStore

[tdipisa]

Description

We need to migrate GeoStore and Http-Proxy into MapStore repository and improve the MapStore's maven build to include them accordingly.

• The MS Jenkins jobs need to be updated accordingly (@randomorder)
• The MS Dev guide need to be updated accordingly (@axl8713)
• The MapStore project should be revised a bit in its directory structure for related build and development purposes (@axl8713)
• Migrate GeoStore and Http-Proxy opened issue in MapStore assigning a proper label to distinguish them (HttpProxy and GeoStore) (@MariaBanti @tdipisa)
• Migrate relevant WIKI pages of GeoStore and Http-Proxy harmonizing them in the existing MS Dev guide (@offtherailz @tdipisa)

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)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe: Related DEV Guide documentation updates

Other useful information

We can also consider having additional maven profiles or reviewing the existing ones for the purpose of this task.