Certificate manager update description for scope property certificate resource

[Hamzawy63]

• Updated the description of the scope field in certificate resource to reflect that a new value, ALL_REGIONS, is now supported.
• Modified an example to use scope=ALL_REGIONS.
• Some of the resources names in the tests weren't identified using variables. That caused "resource already exists" error whenever I ran all acceptance tests for CCM at once(make testacc TEST=./google TESTARGS='-run=TestAccCertificateManagerCertificate'). Adding them to variables will make TF add a random suffix to the names when It creates the resources and hence avoid concurrency issues.

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
• Ran relevant acceptance tests using my own Google Cloud project and credentials (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read Write release notes before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

certificatemanager: updated the description of the `scope` field in `certificate` resource to show that ALL_REGIONS is supported 

[modular-magician]

Hello! I am a robot. It looks like you are a community contributor. @trodge, 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.

You can help make sure that review is quick by doing a self-review and by running impacted tests locally.

[Hamzawy63]

ALL_REGIONS hasn't been added yet to the api docs. Though, It should be visible by the time this PR got merged.

Also, the scope is defined as an ENUM in the api page, but It's a sting in TF. is changing it from string to ENUM going to be a breaking a change?

[trodge]

Yes, changing a string to an enum would be a breaking change.

[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 ( 5 files changed, 19 insertions(+), 16 deletions(-))
Terraform Beta: Diff ( 5 files changed, 19 insertions(+), 16 deletions(-))
TF OiCS: Diff ( 3 files changed, 7 insertions(+), 7 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2949
Passed tests 2638
Skipped tests: 302
Affected tests: 9

Action taken

Found 9 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccBigQueryDataTable_bigtable|TestAccBigtableAppProfile_bigtableAppProfileAnyclusterExample|TestAccBigtableAppProfile_bigtableAppProfileMulticlusterExample|TestAccBigtableAppProfile_bigtableAppProfileSingleclusterExample|TestAccCertificateManagerCertificate_certificateManagerSelfManagedCertificateExample|TestAccCertificateManagerCertificate_certificateManagerGoogleManagedCertificateIssuanceConfigExample|TestAccCertificateManagerCertificateIssuanceConfig_certificateManagerCertificateIssuanceConfigExample|TestAccDataSourceGoogleServiceAccountJwt|TestAccFolderIamPolicy_basic

Get to know how VCR tests work

[modular-magician]

$\textcolor{green}{\textsf{Tests passed during RECORDING mode:}}$
TestAccBigQueryDataTable_bigtable[Debug log]
TestAccBigtableAppProfile_bigtableAppProfileAnyclusterExample[Debug log]
TestAccBigtableAppProfile_bigtableAppProfileMulticlusterExample[Debug log]
TestAccBigtableAppProfile_bigtableAppProfileSingleclusterExample[Debug log]
TestAccCertificateManagerCertificate_certificateManagerSelfManagedCertificateExample[Debug log]
TestAccCertificateManagerCertificate_certificateManagerGoogleManagedCertificateIssuanceConfigExample[Debug log]
TestAccCertificateManagerCertificateIssuanceConfig_certificateManagerCertificateIssuanceConfigExample[Debug log]
TestAccDataSourceGoogleServiceAccountJwt[Debug log]
TestAccFolderIamPolicy_basic[Debug log]

Rerun these tests in REPLAYING mode to catch issues

$\textcolor{green}{\textsf{No issues found for passed tests after REPLAYING rerun.}}$

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$\textcolor{green}{\textsf{All tests passed!}}$
View the build log or the debug log for each test