Add disappears acceptance test for index resource.

[skyscrapr]

Problem

Add disappears test for index to handle scenarios where the index is deleted manually from the console.

Solution

There is a common pattern use in the terraform provider for AWS: docs

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

Test output :
Running tool: /opt/homebrew/bin/go test -timeout 300s -run ^TestAccIndexResource_dimension$ github.com/pinecone-io/terraform-provider-pinecone/pinecone/provider

ok github.com/pinecone-io/terraform-provider-pinecone/pinecone/provider 12.636s

[skyscrapr]

closes #6

[haruska]

@skyscrapr can you rebase this with main? I improved the GH Action workflow to allow approval of acceptance testing with secrets.