* 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
* Part 1: OpenIddict - Minor Changes & Config prep
* add missing nuget
* pr changes
* pr fixes
* remove config for openid -- no need for it for now
* remove unused extension
* Add tests
* use pay tester http client
* check redirecturl in tests
* Adjusted mechanism for setting https binding configuration option.
* Modified the https binding logic to use default bind and port options.
* Removed dedicated https certification config properties and instead used direct access via setting name.