fix: prebuild @parcel added

[jacob-brown]

Issue #, if available: Error during Amplify build: Error(No prebuild or local build of @parcel/watcher found. Tried ${name}. Please ensure it is installed (don't use --no-optional when installing with npm)`

@parcel/watcher needs a prebuild step, possibly due to the use of --no-optional.

Description of changes: Added a prebuild execution for installing @parcel/watcher. Added to package.json to ensure the packages are correctly updated. Execution of prebuild within amplify.yml

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