feat(apigee): google_apigee_instance datasource

[YpNo]

Fixes : #15287

Enabling datasource creation in the instance Template.

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`google_apigee_instance`

[github-actions]

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[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 ( 6 files changed, 478 insertions(+), 14 deletions(-))
google-beta provider: Diff ( 6 files changed, 478 insertions(+), 14 deletions(-))
Open in Cloud Shell: Diff ( 4 files changed, 134 insertions(+))

[modular-magician]

Tests analytics

Total tests: 74
Passed tests: 35
Skipped tests: 37
Affected tests: 2

Click here to see the affected service packages

• apigee

Action taken

Found 2 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

• TestAccApigeeEndpointAttachment_apigeeEndpointAttachmentBasicExample
• TestAccDataSourceApigeeInstance_basic

Get to know how VCR tests work

[modular-magician]

🔴 Tests failed during RECORDING mode:
TestAccApigeeEndpointAttachment_apigeeEndpointAttachmentBasicExample [Error message] [Debug log]
TestAccDataSourceApigeeInstance_basic [Error message] [Debug log]

🔴 Errors occurred during RECORDING mode. Please fix them to complete your PR.

View the build log or the debug log for each test