Add in-app updater structure with markdown rendering

[Francesco146]

Introduce a framework for an in-app updater, including UI elements for checking updates and displaying update information. This enhances user experience. this is my first time dealing with swift (and iOS / macOS development).. so expect some issues :_) . i wanted to put a starting base since the feature is quite usefull and the issue is very old. thanks to those who will do the code review :)

Closes: #3378

[osy]

Have you tested it?

[Francesco146]

yes, it compiles and renders the correct markdown. I'll send screenshots to show off the changes. the changes lay off a base for some future security checks, but i can remove it

[osy]

No I mean does the update actually work?

[Francesco146]

I'll need more testing on that. i tested these scenarios in ios and macos:

• update available detection
• changelog rendering
• skip version and remind me later
• download of the update

for ios it stops there, just prompts the user to the apple store or the guide for sideloaded apps. for macos i need to test the installation process. I'll let you know as soon as i have the time!

[Francesco146]

due to my various commitments, i'm no longer able to follow up on this PR. after my latest changes, i gave up on automatic installation of updates and decided to simplify things by notifying the user of the availability of a new version and displaying the changelog. i have tested my changes on my mac and on a simulated iphone, and they work as expected. i think the code could be simplified considerably, given that the original plan was much larger than it is at the moment. in any case, i'm marking this PR ready for review, and i'm available to give write access to any reviewers