dhis2: Remove discover and switch to async/await

[hunterachieng]

Summary

This PR extends the work of #1059 (which was merged early)

Fixes #51 #1047 #975 #1049 #1036

Details

This PR focused on:

• Remove discover() function
• Switch to async/await
• Bump axios version to 1.8.2
• Implement better upsert() multiple entinties error
• Fixed get with parseAs:base64
• Update state docs in jsDoc

AI Usage

Please disclose how you've used AI in this work (it's cool, we just want to
know!):

• Code generation (copilot but not intellisense)
• Learning or fact checking
• Strategy / design
• Optimisation / refactoring
• Translation / spellchecking / doc gen
• Other
• I have not used AI

You can read more details in our
Responsible AI Policy

Review Checklist

Before merging, the reviewer should check the following items:

• Does the PR do what it claims to do?
• If this is a new adaptor, added the adaptor on marketing website ?
• If this PR includes breaking changes, do we need to update any jobs in
  production? Is it safe to release?
• Are there any unit tests?
• Is there a changeset associated with this PR? Should there be? Note that
  dev only changes don't need a changeset.
• Have you ticked a box under AI Usage?

[josephjclark]

@hunterachieng not all of these changes are major

It's ok to create multiple changeset files. You can have a 100 changes, created indivdually, no problem at all.

I'll fix this in the final changelog for the adaptor so no action needed now. But in future, good practice is to create a changeset every time you finish a feature that will affect users.