update legacy term: Terraform Cloud agent => HCP Terraform Agent

[latentd]

I've updated the legacy term Terraform Cloud agent to HCP Terraform Agent, which was used in error messages.

Target Release

1.12.x

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.

[hashicorp-cla-app]

All committers have signed the CLA.

[crw]

Thanks for this submission! I will raise it in triage this week.

[uturunku1]

Thank you for this update!

[latentd]

@uturunku1 Thanks for kindly reviewing! Since I’m not authorized to deploy to Vercel and pass all CI tests, I’d appreciate it if you could test and merge this PR as needed.

[crw]

Hi @latentd, this is close. I've asked for help with the failing test. Once that gets resolved it will get merged. Thanks for your contribution!

[latentd]

@crw Thank you for your support! I really appreciate it.

[github-actions]

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