Migrate to Nornir 3.x and refactor inventory to support multiple SOT

[dgarros]

This PR is refactoring how the project is managing the inventory to allow multiple inventories to coexist.
In the process, I upgraded Nornir to the latest version.

I moved the inventory for Netbox IN network_importer.adapters.netbox_api and I created a similar inventory for Nautobot as well.

Also, I started to remove the license at the top of some files to align with other NTC projects but I haven't checked all files.

I think we should be good to merge this PR into add_nautobot when the tests are passing but here is a list of TODO that we need to address before merging into develop:

• Add unit tests for Nautobot inventory
• Add integration tests for Nautobot
• Update the documentation with the latest changes regarding the inventory
• Remove the reference to the license from all files, to align with other NTC project

Configuration File Changes

[inventory]

• fqdn, filter and use_primary_ip have been removed from the inventory section, these settings are now part of the NetboxAPIInventory settings
• supported_platforms has been moved to the inventory section, it was previously under [netbox]
• a new section [inventory.settings] is available and everything in this section will be passed to the inventory class at runtime. This allow each inventory to define and validate its own settings.

[netbox] & [nautobot]

Both sections have been removed from the main configuration and are now defined within each adapter under network_importer.adapters.ADAPTER_NAME.settings

[adapters]

• network_params has been renamed to network_settings
• sot_params has been renamed to sot_settings

[jvanderaa]

Minor update that would not be harmful to merge in.