[flutter_tools] add sdk constraint to plugin/package templates (#60932)

Gives plugin and package a constraint on the flutter version, which will be from 2 stable's ago when this goes to stable. Adds an upper bound of 2.0
diff --git a/packages/flutter_tools/templates/package/pubspec.yaml.tmpl b/packages/flutter_tools/templates/package/pubspec.yaml.tmpl
index a2b89fd..6a56bd9 100644
--- a/packages/flutter_tools/templates/package/pubspec.yaml.tmpl
+++ b/packages/flutter_tools/templates/package/pubspec.yaml.tmpl
@@ -6,6 +6,7 @@
 
 environment:
   sdk: ">=2.7.0 <3.0.0"
+  flutter: ">=1.17.0 <2.0.0"
 
 dependencies:
   flutter:
diff --git a/packages/flutter_tools/templates/plugin/pubspec.yaml.tmpl b/packages/flutter_tools/templates/plugin/pubspec.yaml.tmpl
index fb93073..c9b90de 100644
--- a/packages/flutter_tools/templates/plugin/pubspec.yaml.tmpl
+++ b/packages/flutter_tools/templates/plugin/pubspec.yaml.tmpl
@@ -6,7 +6,7 @@
 
 environment:
   sdk: ">=2.7.0 <3.0.0"
-  flutter: ">=1.10.0"
+  flutter: ">=1.17.0 <2.0.0"
 
 dependencies:
   flutter: