Make the JSON view for init commands use defaults from the hclog package

[SarahFrench]

Related to #37818

The logs from init include timestamps in format time.RFC3339 while other JSON logs use hclog.TimeFormat format.

This discrepancy is due to the logging implementation in #34886 avoiding hclog and instead printing a JSON string to the view's streams. If hclog was used directly then the calling code would not need to set a value for the timestamp and influence its format.

We can't get context from participants in the original PR to know why printing a JSON string was chosen and what limitations that might have been attempting to overcome. This PR assumes that there weren't any limitations and it was just unfamiliarity with hclog, which may or may not be true.

Regardless of why logging was implemented like that, making a change in the timestamp format may affect any systems consuming the logs, and at a minimum would require:

• Checking that there's no breaking change in HCP Terraform.
• Checking for required updates to terraform-exec and terraform-json.

These concerns have been addressed, see #37818 (comment)

Target Release

1.15.x

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

CHANGELOG entry

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

[mildwonkey]

👍🏻 really nice investigative / proof-of-non-breakage work associated with this!

[github-actions]

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