added support us-isob-west-1 region

[jdwtf]

Description

I added the necessary bits to enable eksctl to work on clusters in the us-isob-west-1 region.

Checklist

• [N/A] Added tests that cover your change (if possible) - testing for isolated regions is by partition and existing testing for us-isob-east-1 region covers this
• Added/modified documentation as required (such as the README.md, or the userdocs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes
• (Core team) Added labels for change area (e.g. area/nodegroup) and kind (e.g. kind/improvement)

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[jdwtf]

addresses #8594