Code Refactoring to Allow other implementation like Git Sync , Import Export

[shanalikhan]

Need to refactor the code similar to #822.

More generic code to allow anyone to add users to integrate their own Implementations.
Currently, only gist sync is allowed. Once the code is refactored with proper interfaces users can add their own implementations for:

1. Git Repo Sync - Allow users to push and pull from the repo
2. File Import / Export - Allow users to import / export settings from Settings Sync.

These are the implementations that are most wanted but need code refactoring to allow users to implement their services classes to make Settings Sync compatible with any service they want.

cc : @knyhle @arnohovhannisyan

Edit

Anyone who wants to attempt it should use PR #937 as a baseline, then start working on it furthermore as a refactoring.

[shanalikhan]

The current version is defined in Global Settings and environmentPath file and in the release notes of UI. We need to replace them and let extension read the current version from package extension manifest file , api provided by code