Fix id validation for custom service and SLO to match what's actually usable

[pokutuna]

Fixes hashicorp/terraform-provider-google#15825

The validation for the following id fields were too strict, so they have been adjusted to match the actual formats. Please refer to the issue for specific examples.

• service_id on google_monitoring_custom_service
• slo_id on google_monitoring_slo

I checked this documentation. Types of breaking changes | Magic Modules
This change relaxes the validation to contain the current pattern, so I think this is not a breaking change.

Do I need to add tests for the validation defined in regex? If so, I'll add it.
It would be helpful if you could advise on existing test cases for such a change.

Release Note Template for Downstream PRs (will be copied)

monitoring: fixed validation of `service_id` on `google_monitoring_custom_service` and `slo_id` on `google_monitoring_slo` 

[modular-magician]

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@NickElliot, 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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[NickElliot]

LGTM! Thanks for the update.

[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.

Terraform GA: Diff ( 3 files changed, 7 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 2 files changed, 2 insertions(+), 2 deletions(-))

[modular-magician]

Tests analytics

Total tests: 3037
Passed tests 2739
Skipped tests: 297
Affected tests: 1

Action taken

Found 1 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccDataprocClusterIamPolicy

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[modular-magician]

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