Resolves #52

Summary

Adds support for managing global SNMP configurations in the Inventory App, including:

• CRUD operations for global SNMP settings
• Label-based lookup and assignment helpers
• Integration into the device configuration model (ID + activation flag)

This enables assigning reusable SNMP configurations to devices in a lightweight and consistent way.

Example: Assign SNMP config to a device by label

Assuming a global SNMP configuration named "SNMP Config for eMerge" has already been created via the Inventory App GUI:

label = "SNMP Config for eMerge"
snmp_setting_id = app.inventory.get_global_snmp_config_id_by_label(label)
device_config.set_global_snmp_setting(snmp_setting_id)

Optional: store the reference only (without activating it yet):

device_config.set_global_snmp_setting(snmp_setting_id, activate=False)

To verify assigned config:

device_config.get_global_snmp_setting_id()
# > ab949038-9dc4-4fc7-af4f-cba04584e686

snmp_setting_label = app.inventory.get_global_snmp_config_label_by_id("ab949038-9dc4-4fc7-af4f-cba04584e686")
print(snmp_setting_label)
# > SNMP Config for eMerge