add option to specify endpoint for AWS Provider

[piotrkpc]

Description

This PR adds a configuration option to the AWS provider to specify Endpoint for AWS Route53 client used in AWS Provider. It will help write more comprehensive e2e tests with tools such as Localstack or external stubs of Route53 API.
It does not change API or add configuration options exposed to the user.

Add Endpoint configuration option for AWSConfig used by AWS Provider.

Checklist

• Unit tests updated - N/A
• End user documentation updated - N/A

[szuecs]

/ok-to-test

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This pull-request has been approved by: mloiseleur, piotrkpc
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[piotrkpc]

@mloiseleur This is no longer needed as the code was nicely refactored by @johngmyers as part of #3648 in 794a10d

[ezraroi]

@piotrkpc How can we control this without code? Looks like the AWS endpoint is not configured from file or ENV var.
Looks like AWS Go SDK V2 is supporting this, while V1 which is used does not
https://docs.aws.amazon.com/sdkref/latest/guide/feature-ss-endpoints.html#ss-endpoints-sdk-compat

[piotrkpc]

@ezraroi not sure, I've not been following the code lately but the latest version should work. AWS GO SDK v1 also can take endpoint from env variables. https://docs.aws.amazon.com/sdkref/latest/guide/feature-endpoint-discovery.html

[ezraroi]

@piotrkpc Thanks but i am not sure it is possible to override the Route53 address this way