Performance: Added request cache to media type retrieval in media picker validation#20405

AndyButland merged 2 commits intomainumbraco/Umbraco-CMS:mainfrom

v16/improvement/cache-media-type-lookups-in-media-picker-validatorumbraco/Umbraco-CMS:v16/improvement/cache-media-type-lookups-in-media-picker-validatorCopy head branch name to clipboard