Add connection_mode field to OpenSearch outbound connection resource

[DanielRieske]

Description

This PR adds a way to specify the connection mode (Direct or VPC Endpoint).

Adding this feature did present a challenge on how to output the VPC Endpoint URL.
This field is only set when the connection has been accepted and because this is currently done with a separate resource the aws_opensearch_inbound_acceptor, we can't reliably set this field.

To solve this issue, I added an additional parameter called accept_connection to merge the funtionality from the acceptor in this resource.

This offers the following benefits,

• Reduces complexity of having multiple resources.
• Have the endpoint field set immediately after creating the resource.

If this PR gets merged I will create an additional PR to deprecate the aws_opensearch_inbound_acceptor resource.
I can't remove it in this PR as it would introduce a breaking-change.

Relations

Closes: #32630

References

Output from Acceptance Testing

terraform-provider-aws git:(f-aws_opensearch_outbound_connection_mode_attribute) make testacc TESTS=TestAccOpenSearchOutboundConnection_ PKG=opensearch
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/opensearch/... -v -count 1 -parallel 20 -run='TestAccOpenSearchOutboundConnection_'  -timeout 180m
=== RUN   TestAccOpenSearchOutboundConnection_basic
=== PAUSE TestAccOpenSearchOutboundConnection_basic
=== RUN   TestAccOpenSearchOutboundConnection_vpc
=== PAUSE TestAccOpenSearchOutboundConnection_vpc
=== RUN   TestAccOpenSearchOutboundConnection_disappears
=== PAUSE TestAccOpenSearchOutboundConnection_disappears
=== CONT  TestAccOpenSearchOutboundConnection_basic
=== CONT  TestAccOpenSearchOutboundConnection_disappears
=== CONT  TestAccOpenSearchOutboundConnection_vpc
--- PASS: TestAccOpenSearchOutboundConnection_basic (2008.36s)
--- PASS: TestAccOpenSearchOutboundConnection_disappears (2040.62s)
--- PASS: TestAccOpenSearchOutboundConnection_vpc (2514.09s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/opensearch 2516.093s

...

[github-actions]

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[ewbankkit]

LGTM 🚀.

% make testacc TESTARGS='-run=TestAccOpenSearchOutboundConnection_' PKG=opensearch ACCTEST_PARALLELISM=2
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./internal/service/opensearch/... -v -count 1 -parallel 2  -run=TestAccOpenSearchOutboundConnection_ -timeout 360m
=== RUN   TestAccOpenSearchOutboundConnection_basic
=== PAUSE TestAccOpenSearchOutboundConnection_basic
=== RUN   TestAccOpenSearchOutboundConnection_vpc
=== PAUSE TestAccOpenSearchOutboundConnection_vpc
=== RUN   TestAccOpenSearchOutboundConnection_disappears
=== PAUSE TestAccOpenSearchOutboundConnection_disappears
=== CONT  TestAccOpenSearchOutboundConnection_basic
=== CONT  TestAccOpenSearchOutboundConnection_disappears
--- PASS: TestAccOpenSearchOutboundConnection_disappears (2085.93s)
=== CONT  TestAccOpenSearchOutboundConnection_vpc
--- PASS: TestAccOpenSearchOutboundConnection_basic (2301.50s)
--- PASS: TestAccOpenSearchOutboundConnection_vpc (2808.15s)
PASS
ok  	github.com/hashicorp/terraform-provider-aws/internal/service/opensearch	4899.251s

[ewbankkit]

@DanielRieske Thanks for the contribution 🎉 👏.

[github-actions]

This functionality has been released in v5.19.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.