[Tooling] GitHub to GitLab demo app migration

[pylapp]

Description

Today the whole project is hosted on GitHub, under MIT open source license, except the CI/CD chain.
However the aim of OUDS is to expose also some brand themes like, we hope, Sosh, Parnasse, Innovation Cup, or other themes, and these themes may remain closed source under proprietary license and hosted in our internal GitLab forges so as to not expose assets, fonts, images or other resources.

Thus, we will have to make a migration, maybe for the v1 release, to GitLab for the demo app and keep there the CI/CD chain.
Today only alpha, beta and prod builds are made in our own runners in internal forge so as to keep the Apple certificates secrets and localy stored.

Because the update of the CI/CD chain and the migration of projects is a boring, time consuming and heavy task, it mmust be done if and only if some prerequisites are filled.

Definition of Ready

• Have a final name for the demo app ([Demo App] Renaming of demo application #85)
• Have the icons for alpha, beta, prod releases ([Demo App] Update the app icon with the new launch icon #140)
• Split alpha, beta and prod releases (i.e. change bundle identifiers) ([Demo App] Create a separate alpha release version #141 )
• Do not have big changes on going so as to prevent complexe rebase betwen branches

Definiton of Done

• Create in our GitLab a new project hosting the demo app
• Make the demo app use the suitable branch of OUDS (maybe develop ?)
• Update the CI/CD chain to build for alpha, beta and prod versions (beware with alpha release! reference to OUDS Swift Package ust be change in the project settings. Maybe use XCConfig file or stuff like that?)
• Prune the GItHub project so as to convert it as a "pure" Swift Package project, without demo app

[pylapp]

blocking beecause prerequisites are not filled, see definition fo ready

[pylapp]

cc @B3nz01d @ludovic35

[pylapp]

on hold as this is not mandatory at all, move to GitLab will imply to refactor the CI/CD pipelines and find workarounds for the alpha releases where the app will have to point to the SDK with the needed branch to test. Or maybe we will have to ensure the app will point to whatever the branch of the lib is, but in its own branche to compile.