Add melos and cleanup gitignore and pubspec.lock

[TahaTesser]

Cleanup gitignore and pubspec.lock

Whenever I execute flutter pub get in the main folder and the examples, it generrates a whole of bunch of pubspec.lock which should be ignored in the first place but I took the next step and added melos to this repository.

wolt_modal_sheet is a monorepo with a components package and non-standard examples.

├── .github
│   └── workflows
├── coffee_maker  <-  (pubspec.lock inside this should be ignored)
├── demo_ui_components  <-  (pubspec.lock inside this should be ignored)
├── doc
├── example <- (pubspec.lock inside this should be ignored)
├── lib
├── playground  <- (pubspec.lock inside this should be ignored)
├── playground_navigator2  <- (pubspec.lock inside this should be ignored)
├── test
├── .gitignore
├── CHANGELOG.md
├── LICENSE
├── README.md
├── analysis_options.yaml
├── pubspec.lock <- (should be ignored)
├── pubspec.yaml

melos

Added melos which will help to execute commands in the root and subfolders. This can be expanded in the future to do more than pub get. At the moment, melos bootstrap execute flutter pub get in the root and all the subfolders and get the project ready to work.

Before this PR (bunch of files in the git tree)

After this PR (clean git tree)

[ulusoyca]

Thank you Taha! Indeed this was a problem. Thanks for introducing Melos