Remove build image reference from release workflow, consolidate go setup in GitHub actions

[bryantbiggs]

Description

• Remove container: public.ecr.aws/eksctl/eksctl-build:... references; this image is no longer used and does not appear to have any bearing on the CI release process - the artifacts will be build directly in the GitHub runner environment
• Consolidate the misc actions/cache actions for caching go depdencies - this is already handled by the internal .github/actions/setup-build action
• Consolidate the misc actions/setup-go actions for installing go - this is already handled by the internal .github/actions/setup-build action which means less places to remember to update the go version in the future
• Remove the secrets.EKSCTLBOT_TOKEN usage from actions/checkout - this should be necessary given that the code is publicly available

⚠️ this can only proceed once the changes in #8157 are added back to main

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 🌟