feat(js/plugin/compat-oai): add support to input pdfs or base64 files

[xavidop]

Description here... Help the reviewer by:

• Adds the ability to process documents in the OpenAI plugin
• Fixes this issue: [JS] Bug in OpenAI Compatible API plugin: Not supporting non-image files #3917

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[xavidop]

@pavelgj can you have a look at this one?

[ssbushi]

Left a couple of small comments.

Thanks @xavidop!

[xavidop]

@ssbushi, the PR is ready to re-review! :)