IM-731 Rename mc-app application type to merchant-center-custom-application

[harm-meijer]

Link to the Jira issue

IM-731

Description and context

Rename mc-app application type to merchant-center-custom-application

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Brief description of the solution

How was it tested?

Instructions to build/test locally

Depends on another PR/branch?

• No
• Yes - dependant on connnect-services

Checklist-

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• I joined a screenshot of the app before and after the fix.

[upload the screenshot here]

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Latest commit: 3bef575

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