KTX2 Compression for Thumbnails, Envmaps

[AidanCaruso]

Summary

Adds ktx2 compression to thumbnails and envmaps.

References

closes #insert number here

Checklist

• If this PR is still a WIP, convert to a draft
• When this PR is ready, mark it as "Ready for review"
• ensure all checks pass
• Changes have been manually QA'd
• Changes reviewed by at least 2 approved reviewer

QA Steps

List any additional steps required to QA the changes of this PR, as well as any supplemental images or videos.

[HexaField]

Rather than changing all our logic to ktx2, we should add options to support multiple file types.

[AidanCaruso]

Rather than changing all our logic to ktx2, we should add options to support multiple file types.

This makes sense for thumbnails, I'll add backwards compatibility there (and you can still load pngs as envmaps).

changes implemented