nk3: Add get-config and set-config subcommands

[robin-nitrokey]

This PR adds the nk3 get-config and nk3 set-config subcommands to access the device configuration of a Nitrokey 3.

Checklist

Make sure to run make check and make fix before creating a PR, otherwise the CI will fail.

• tested with Python3.9
• signed commits
• updated documentation (e.g. parameter description, inline doc, docs.nitrokey)
• added labels

Test Environment and Execution

• OS: Debian 11
• device's model: NK3AM
• device's firmware version: Add basic config mechanism for fido2 nitrokey-3-firmware#337 (3f976bcb35716515828cec4683241f21d6792810)

Relevant Output Example

$ nitropy nk3 get-config fido.disable_skip_up_timeout                                                                                                                                                                                               
Command line tool to interact with Nitrokey devices 0.4.39                                                                                                                                                                                                                                
false                 

$ nitropy nk3 set-config fido.disable_skip_up_timeout true                                                                                                                                                                                          
Command line tool to interact with Nitrokey devices 0.4.39                                                                                                                                                                                                                                
Updated configuration fido.disable_skip_up_timeout.

$ nitropy nk3 get-config fido.disable_skip_up_timeout                                                                                                                                                                                               
Command line tool to interact with Nitrokey devices 0.4.39                                                                                                                                                                                                                                
true   

[daringer]

lgtm!