Fix for "Keep the remote version" deletes files on new development theme

[mgmanzella]

WHY are these changes introduced?

Fixes #2433

WHAT is this pull request doing?

• Adds @created_at_runtime variable that gets set to true if development theme is created
• Defaults to using local files @created_at_runtime=true

How to test your changes?

New development themes defaults to local files

• In your partners dashboard, create a new dev store
• Create a new staff account for your work email if your partners account isn't associated with your work email (you need to do this so you can you use the cli with the new store)
• Accept invite for staff account

In a new terminal

$ shopify theme init
$ cd <name of theme>
$ git init
$ git add —all
$ git commit -am "init"
$ pwd

Copy the path printed after pwd

In another terminal

$ git fetch
$ git checkout fix-remote-file-local-delete
$ shopify-dev login —store <new store name>
$ shopify-dev theme serve </Path/to/theme/ that you copied> --theme-editor-sync

Confirm local files get uploaded and don't get deleted. Some files do get updated locally though

Existing development theme prompts user for strategy

In the theme directory run git reset --hard to restore the files. In the shopify-cli directory run shopify-dev theme serve </Path/to/theme/> --theme-editor-sync again and confirm you're prompted to pick a sync strategy

Post-release steps

None

Update checklist

• I've added a CHANGELOG entry for this PR (if the change is public-facing)
• I've considered possible cross-platform impacts (Mac, Linux, Windows).
• I've left the version number as is (we'll handle incrementing this when releasing).
• I've included any post-release steps in the section above (if needed).

[karreiro]

Thank you, @mgmanzella! Elegant PR 🚀

I've left one minor/optional comment to clarify a detail, but the PR looks good and works fine as well 🎩

Thanks!