Klaytn -> Kaia in local variables, strings

[ian0371]

Proposed changes

This PR is based on #2152. This PR renames local variables and must NOT have any effect.
LOC containing klay: (dev) 7415 -> (#2152) 4442 -> (#2155) 3502

Types of changes

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• Bugfix
• New feature or enhancement
• Others

Checklist

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• I have read the CONTRIBUTING GUIDELINES doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes ($ make test)
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Further comments

$ rg -i klay | rg -v github.com | rg -vi license | rg -vi modif | rg -vi copyright | rg -vi library | rg -v TODO-Klaytn-Issue | wc
   3502   26585 1279889