Add issue templates, contribution guidelines, and code of conduct; update CI/CD workflows and project metadata

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

.gitignore

@@ -1,7 +1,38 @@
-# https://dart.dev/guides/libraries/private-files
-# Created by `dart pub`
-.dart_tool/
+# See https://www.dartlang.org/guides/libraries/private-files
 
-# Avoid committing pubspec.lock for library packages; see
-# https://dart.dev/guides/libraries/private-files#pubspeclock.
+# Files and directories created by pub
+.dart_tool/
+.packages
+# If you're building an application, you may want to check-in your pubspec.lock
 pubspec.lock
+*.g.dart
+
+# Directory created by dartdoc
+# If you don't generate documentation locally you can remove this line.
+doc/api/
+
+# dotenv environment variables file
+.env*
+
+# Build files
+build/
+.idea/
+*.iml
+
+# Avoid committing generated Javascript files:
+*.dart.js
+# Produced by the --dump-info flag.
+*.info.json
+# When generated by dart2js. Don't specify *.js if your
+# project includes source files written in JavaScript.
+*.js
+*.js_
+*.js.deps
+*.js.map
+
+.flutter-plugins
+.flutter-plugins-dependencies
+
+# OS generated files
+.DS_Store
+Thumbs.db