Fix image download headers regresison and fix png image issue

[wanliAlex]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  bug fix

• What is the current behavior? (You can also link to an open issue here)
  This is a regression as image_download_headers. Private images can not be downloaded even if users passes image_download_headers. Thi is a regression.

We also find an issue that when providing weighted queries, Marqo can not accept a queries with more than 2 modalities. An 500 error is raised:

res = mq.index("test").search({"test": 1, "https://marqo-k400-video-test-dataset.s3.amazonaws.com/videos/-LenAZs2OFM_000002_000012.mp4": 1, "https://raw.githubusercontent.com/marqo-ai/marqo/mainline/examples/ImageSearchGuide/data/image1.jpg": 1})


Languagebind models can't take `.png` images as input.

• What is the new behavior (if this is a feature change)?

• We introduce a new parameter, mediaDownloadHears and will deprecate imageDownloadHeaders in the future.
• We fix the regression. Users can add documents with private images by providing media_download_headers.
• Fix the bug that users can not provide more than 2 modalities in the weighted query.
• Fix the bug that languagebind models can't take .png images as input. It can not index .png models correctly.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

• Have unit tests been run against this PR? (Has there also been any additional testing?)

• Related Python client changes (link commit/PR here)

• Related documentation changes (link commit/PR here)

• Other information:

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added / updated (for bug fixes / features)