Make (R)IGM.PerInstanceConfigs lock on Instance name, not IGM

[askubis]

Allow parallelization of per instance config related operations by not locking on the IGM
Fixes b/270736647

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compute: Allow parallelization of google_compute_(region_)per_instance_config by not locking on the parent resource, but including instance name.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 2 files changed, 4 insertions(+), 4 deletions(-))
google-beta provider: Diff ( 2 files changed, 4 insertions(+), 4 deletions(-))

[modular-magician]

Tests analytics

Total tests: 1096
Passed tests: 1021
Skipped tests: 75
Affected tests: 0

Click here to see the affected service packages

• compute

🟢 All tests passed!

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[github-actions]

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@BBBmau, a repository maintainer, has been assigned to review your changes. If you have not received review feedback within 2 business days, please leave a comment on this PR asking them to take a look.

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[BBBmau]

approving since this follows the mutex format in docs: https://googlecloudplatform.github.io/magic-modules/reference/resource/#mutex