EZEE-3486: Added AllowedContentTypes to default config as it was overridden by default empty value

[ViniTou]

Question	Answer
Tickets	https://issues.ibexa.co/browse/EZEE-3486
Bug fix?	yes
New feature?	no
BC breaks?	no
Tests pass?	yes
Doc needed?	no
License	GPL-2.0

This had nothing to do with unsplash, or dam connector.
From what I understand allowed CTs were passed here ezplatform-admin-ui/src/bundle/Resources/public/js/scripts/fieldType/ezimageasset.js L178

            ReactDOM.render(
                React.createElement(eZ.modules.UniversalDiscovery, {
                    onConfirm,
                    onCancel,
                    title,
                    allowedContentTypes: [imageAssetMapping['contentTypeIdentifier']],
                    ...config,
                }),
                udwContainer
            );

But since that key now exist with default value, this part is overridden by it.

Checklist:

• Coding standards ($ composer fix-cs)
• Ready for Code Review

[adamwojs]

@ViniTou Code style needs to be fixed here.

[tomaszszopinski]

QA approved on Ibexa DXP 3.2.5-dev & 3.3.2-dev with patch.

[lserwatka]

Could you merge it up?