[BREAKING_CHANGES] fix: support ThreadMessage.Content as an array

[adamdecaf]

Describe the change
FileIDs on ThreadMessage isn't supported anymore, but Content can be an array.

Provide OpenAI documentation link
https://platform.openai.com/docs/api-reference/threads/createThread

Describe your solution
Remove old fields and update existing ones to support current OpenAI endpoints.

Tests
I've verified this allows me to upload an image and prompt in a thread (ran under an assistant).

Here's the snippet of code that creates the thread.

	thread, err := c.underlying.CreateThread(ctx, openaiclient.ThreadRequest{
		Messages: []openaiclient.ThreadMessage{
			{
				Role: openaiclient.ThreadMessageRoleUser,
				Content: []openaiclient.ThreadMessageContent{
					{
						Type: "image_file",
						ImageFile: &openaiclient.ThreadMessageImageFile{
							FileID: file.ID,
						},
					},
					{
						Type: "text",
						Text: &prompt,
					},
				},
			},
		},
	})

Fixes: #773

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.01%. Comparing base (774fc9d) to head (d6c7739).
Report is 45 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #821      +/-   ##
==========================================
+ Coverage   98.46%   99.01%   +0.55%     
==========================================
  Files          24       26       +2     
  Lines        1364     1418      +54     
==========================================
+ Hits         1343     1404      +61     
+ Misses         15        8       -7     
  Partials        6        6              

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[sashabaranov]

Hey, thank you for the PR!

The documentation says it is either a string or array: https://platform.openai.com/docs/api-reference/messages/createMessage#messages-createmessage-content

So I think we need a new type here that supports proper marshalling

[adamdecaf]

Could we send an array of one with text: { ... } instead of a new type?

[archimed-shaman]

Hi, guys.
Are there any updates on this PR? It seems like without it, the library can't fully utilize the assistants' API.