Adjust folder structure and upgrade SDK version

[mariamedp]

• Updated folder structure to match the structure agreed between all mlops accelerators in DS Toolkit. To us, this means:

  • Adding an infra folder
  • Renaming operation/execution to mlops for simplicity

• Updated documentation accordingly

• Upgraded SDK version to latest one (1.53) - closes #82

• Added a couple of unit tests

• Changed service connections names to point to new subscription

• Fixed linting issues