Introduce an API to retrieve images from a storage and include authorization headers to the request

[JaneSjs]

T20693 - survey logo needs credentials when generating PDF
https://surveyjs.answerdesk.io/internal/ticket/details/T20693

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SurveyJS PDF requires to retrieve images and convert them to Base64. A survey may contain images which can be downloaded only if a request passes server authorization. However, SurveyJS PDF model doesn't currently provide an API which would allow developers to send a request and retrieve an image for an Image, an Image Picker, or a survey logo.