Better error handling when using `config_context` for secret_access_type.

[itdependsnetworks]

Environment

• Python version: latest
• Nautobot version: latest
• nautobot-plugin-nornir version: latest

Proposed Functionality

Pre-emptivly check, and allow sane error

    access_type_str = device_obj.get_config_context()["nautobot_plugin_nornir"]["secret_access_type"].upper()
KeyError: 'nautobot_plugin_nornir'

Use Case

More clear guidance to the user.