fix: return appropriate error message during webhook call for invalid merchant_secret adyen

[hrithikesh026]

Type of Change

• Bugfix
• New feature
• Enhancement
• Refactoring
• Dependency updates
• Documentation
• CI/CD

Description

Currently adyen returns bad request body error during webhook call if merchant_secret set by the merchant for webhook source verification is invalid.

In this PR, appropriate error message will be returned when merchant_secret is an invalid value.

{"error":{"type":"invalid_request","message":"Merchant Secret set for webhook source verificartion is invalid","code":"WE_02"}}

hex::decode(string) function is used to decode the merchant_secret to a Vec<u8> in adyen.
This hex::decode(string) function will return Err() if the string value passed to it either has odd number of characters or if it has an invalid character.

Additional Changes

• This PR modifies the API contract
• This PR modifies the database schema
• This PR modifies application configuration/environment variables

Motivation and Context

How did you test it?

Manual

Checklist

• I formatted the code cargo +nightly fmt --all
• I addressed lints thrown by cargo clippy
• I reviewed the submitted code
• I added unit tests for my changes where possible
• I added a CHANGELOG entry if applicable