[feature] Add submit-stac.ipynb for data creation & insertion

[Vierod]

Add submit-stac.ipynb for data creation & insertion.

• create a collection
• add an item
• add linked assets (a combination of plain text files and random images)

The json files, text files and images should be present in a mock-data subfolder of the repo.

Initially this can include any-old-data that meets the stac requirements

[Vierod]

https://github.com/stac-api-extensions/transaction