Add Fastlane config and update release workflow for v2

Single unified "Yattee" scheme replaces per-platform schemes.
Release workflow now has toggleable platform inputs instead of
matrix strategy. Standalone mac notarized workflow removed in
favor of the build_mac_notarized toggle. Share extension bundle
ID updated from Open-in-Yattee to ShareExtension.

fastlane/Appfile

@@ -0,0 +1,4 @@
+app_identifier(ENV['DEVELOPER_APP_IDENTIFIER'])
+apple_id(ENV['FASTLANE_USER'])
+itc_team_id(ENV['ITC_TEAM_ID'])
+team_id(ENV['TEAM_ID'])