Support for search by text using OCR in images

NOTE:
**please use english, or include an english translation.** aside from that,
all of the below are optional, consider them as inspiration, delete and rewrite at will

**is your feature request related to a problem? Please describe.**
a description of what the problem is, for example, `I'm always frustrated when [...]` or `Why is it not possible to [...]`

**Describe the idea / solution you'd like**
I think it would be pretty neat if copyparty had the ability to search for images (and maybe videos?) based on their text content. I personally find copyparty very useful for storing my ShareX screenshots and being able to search them for certain text would be a very useful feature. I am unfamiliar with the use of OCR in Python or any available libraries, so I don't know how easy/possible this would be to implement.

**Describe any alternatives you've considered**
a description of any alternative solutions or features you've considered

**Additional context**
add any other context or screenshots about the feature request here

研究用於 Python 整合的 Tesseract 或 pytesseract 等 OCR 函式庫。檢查 copyparty 目前如何為檔案建立索引，以及可以在哪裡加入影像處理。檢查是否已有可擴充的媒體索引器模組。確定如何儲存擷取的文字以支援搜尋查詢，並更新搜尋功能。

由索引模型根據 Issue 內容生成。