NuGet: Added metadata to the Controls project to enable publishing to NuGet

[Lamparter]

Resolved / Related Issues

Discussed on Discord

Steps used to test these changes

1. Built the Files controls project
2. Checked for Roslyn analysers during build
3. Ensured NuGet package was correctly generated
4. Inspected NuGet package internals to ensure proper generation and inclusion of XAML resources

---

WHEN PR IS ACCEPTED (NOT BEFORE)

• Implement actual secret
• Set environment to NuGet

[Lamparter]

Note for reviewer:

The CD fails because there is no such API key provided (please create a NUGET_API_KEY secret in the repository to enable publishing)

[0x5bfa]

We should do this after v4 or even later. What do you think?

[yaira2]

We can move forward with this as soon as the versioning system is agreed on.

[0x5bfa]

If you'd like to publish when you publish preview or stable thru Files CD, we can add a parameter text box to input the version. If empty, don't publish; otherwise, try publish with that version string.

[yaira2]

This shouldn't be tied to app releases. We may have a newer control ready for release before an app update, and on the other hand, we may want to release the app without updating the controls. It's best to handle this as a separate action.