Support `mkdocstrings-python` v2

[llucax]

What's needed?

A new release of mkdocstrings-python v2 is out, and they removed some deprecated stuff that affects us:

• warning: The 'import' key is renamed 'inventories' for the Python handler #357
• paths was moved out of options #483

Proposed solution

• Fix templates to use the inventories and put paths in the right location
• Add a migration script to fix existing projects
• Widen the supported range of versions to allow for v2

Use cases

No response

Alternatives and workarounds

No response

Additional context

• Add support for mkdocstrings-python v2 #481