🐛 DSGECO-1727 fix incorrect config key name

[phawxby]

Description

Fix bug with config validation incorrectly generating error messages omitting the field name segment resulting in the source of configuration problems not being obvious

Test Coverage

• This change is covered by existing or additional automated tests.
• Manual testing has been performed (and evidence provided) as automated testing was not feasible.
• Additional tests are not required for this change (e.g. documentation update).

[acabarbaye]

could you have a test where the field has a mapstructure tag different from the field name
e.g. test {
db string `"mapstructure"="elephant_trunk"
}
the environment variable should be ..._ELEPHANT_TRUNK

[acabarbaye]

thanks for this