fix: remove parent_id from create_experiment

[gt2345]

Description

Follow up for #8927
Since parent id is mostly used internally, and can be confusing for end user when exposed, we decide to remove it from SDK function create_experiment

Test Plan

Commentary (optional)

Checklist

• Changes have been manually QA'd
• User-facing API changes need the "User-facing API Change" label.
• Release notes should be added as a separate file under docs/release-notes/.
  See Release Note for details.
• Licenses should be included for new code which was copied and/or modified from any external code.

Ticket

[netlify]

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 47.15%. Comparing base (17287f5) to head (ed6fd90).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9068   +/-   ##
=======================================
  Coverage   47.15%   47.15%           
=======================================
  Files        1152     1152           
  Lines      141866   141866           
  Branches     2416     2416           
=======================================
  Hits        66897    66897           
  Misses      74779    74779           
  Partials      190      190           

Flag	Coverage Δ
backend	42.99% <ø> (ø)
harness	64.31% <0.00%> (ø)
web	38.92% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...rness/determined/common/experimental/determined.py	41.21% <ø> (ø)
harness/determined/experimental/client.py	55.26% <0.00%> (ø)

[wes-turner]

LGTM