Create in-tree manual section

[adutra]

We already have a good quickstart guide, but at some point a proper manual, divided in sections and covering all possible aspects of this extension, would also be required.

Example of things that are not covered in the quickstart:

• Is the shaded driver jar usable with this extension? see #24
• Is DSE Graph available, and how? See #19, #72, #85
• How to use reactive queries
• How to use continuous paging etc.

┆Issue is synchronized with this Jira Task by Unito

[adutra]

Also:

• Explain the different return types available for DAO methods with Mutiny.