This allows external integrations ( btcpay docker fragments) to highlight specific plugins as recommended to be installed. Also moved the remote option to a config option instead of a url query param to avoid messy situations where users could get deceived with a generated url. The dockerfiles also have an additional csproj to build and the plugin dir was renamed correctly from extensions to plugins
* BTCPay Extensions Part 2
This PR cleans up the extension system a bit in that:
* It renames the test extension to a more uniform name
* Allows yo uto have system extensions, which are extensions but bundled by default with the release (and cannot be removed)
* Adds a tool to help you generate an extension package from a csproj
* Refactors the UI extension points to a view component
* Moves some more interfaces to the Abstractions csproj
* Rename to plugins