Fix panic when embedded type uses a forbidden import

[hariso]

Description

Currently, if a configuration struct has an embedded field that references a type that is not allowed, paramgen panics when trying to return an error that describes the issue and the offending field's name. This is because an embedded field has no explicit field name: https://go.dev/ref/spec#Struct_types.

Quick checks:

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• There is no other pull request for the same update/change.
• I have written unit tests.
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[lovromazgon]

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