docs: added missing --region flag in the for nodegroup and iamidentitymapping pages

[herlon214]

Description

I added the missing --region flag in the docs page for nodegroup and also iamidentitymapping. As pointed in the issue iamidentitymapping by @todd-dsm

Checklist

• Added tests that cover your change (if possible)
• 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 🌟

[Skarlso]

Fine from me! Thank you for your contribution! :)

[Skarlso]

Just waiting for a second pair of eyes. :)

[aclevername]

Thanks @herlon214 !