Validation added to data-dictionary settings page

[kaise-lafrai]

Validation added to data-dictionary settings page to check for existing data dictionary.

fixes [org/repo/issue#]

• Test coverage exists
• Documentation exists

QA Steps

Add manual QA steps in checklist format for a reviewer to perform to confirm that the feature or fix is working. Include as much details as possible so that the reviewer doesn't lose time figuring out how to perform steps.

• log in as an admin
• create a data dictionary at /node/add/data?schema=data-dictionary
• remember the identification you used on the data dictionary page
• navigate to the DKAN > Data-dictionary settings page
• enter an invalid ID and click save
• confirm you get an error message
• enter a valid ID from step 2 and click save
• confirm you get a success message