Begin streamlining default project template.

[jpobst]

Begin streamlining and updating the default project template. There are two goals here:

• Modernize appearance and metadata by removing "Xamarin" branding and verbiage, shifting more towards ".NET for Android" branding.
• Begin making the default project template more generic and configurable via config.json. The desire here is to reduce maintenance burden by making the default template flexible enough that library-specific templates (like kotlin or tink) are no longer required. (Currently we maintain 46 template sets across AndroidX and GPS repos, the majority of which only have minor differences.)

[moljac]

LGTM