FINERACT-1272: Creating Currencies (org.apache.fineract.organisation.monetary.api)

[kapil-panchal]

Description

Describe the changes made and why they were made.

1. Implemented code review comments as per FINERACT-1272: Add the possibility to edit currencies available - Creating Currencies (org.apache.fineract.organisation.monetary.api) #4902
2. Changed the validation messages.

Ignore if these details are present on the associated Apache Fineract JIRA ticket.

Checklist

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• Write the commit message as per https://github.com/apache/fineract/#pull-requests
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• Create/update unit or integration tests for verifying the changes made.
• Follow coding conventions at https://cwiki.apache.org/confluence/display/FINERACT/Coding+Conventions.
• Add required Swagger annotation and update API documentation at fineract-provider/src/main/resources/static/legacy-docs/apiLive.htm with details of any API changes
• Submission is not a "code dump". (Large changes can be made "in repository" via a branch. Ask on the developer mailing list for guidance, if required.)

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