Index UI unit tests

[dmundra]

re: 17377

Describe your changes

Tests for #4185

QA Steps

• [ ] Tests are passing in the pipeline and locally with the following command:

ddev dkan-phpunit \                                                                                                                 
                    --coverage-clover /var/www/html/docroot/modules/contrib/dkan/clover.xml \
                    --coverage-html /var/www/html/docroot/modules/contrib/dkan/coverage-html \
                    --log-junit /var/www/html/docroot/modules/contrib/dkan/junit/junit.xml --filter DataDictionaryWidgetBuildIndexesTest

• [ ] Code coverage for /var/www/html/dkan/modules -> data_dictionary_widget -> src -> Indexes is > 50%