Add support for AWS authentication without assuming a role

[elisiariocouto]

This PR makes the assumedRoleName optional and adds a configuration parameter for the AWS region.

If no assumedRoleName, accessKeyId and accessKeySecret are provided, the AWS Client will be used with no authentication configuration, which in turn will follow the AWS SDK default credential loader.

Related to #98

[emillg]

@elisiariocouto Thanks for your contribution!

Can you explain why you want to set the region other than us-east-1? Because for IAM, region doesn't matter much, and for Cost, it's using us-east-1: https://docs.aws.amazon.com/general/latest/gr/billing.html

[elisiariocouto]

You're right @emillg, just pushed a new commit that removes the region parameter.

[sonarcloud[bot]]

Quality Gate passed

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