Multipart uploads do not properly handle UTF-8 encoded names

https://github.com/adobe/aem-testing-clients/blob/889e1c6fc66ee146c5fa1b526065e36082fc480a/src/main/java/com/adobe/cq/testing/client/CQAssetsClient.java#L394

When building the multipart request, the charset of the filename part is not set as UTF-8 and instead is ISO-8859-1 and the filename characters that are 3-byte UTF-8 (such as Korean and Chinese glyphs) are squashed to ? characters.

Start at src/main/java/com/adobe/cq/testing/client/CQAssetsClient.java around line 394 and inspect how the multipart filename part is built and encoded. Verify the behavior with filenames containing Korean or Chinese characters; done means those UTF-8 characters are preserved instead of becoming question marks.

Written by the indexing model from the issue text.