Added session_duration to the assume_role config

[hamstah]

Fixes #7333

Changes proposed in this pull request:

• Add a session_duration variable in the assume_role configuration block

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccAWSAvailabilityZones'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./... -v -parallel 20 -run=TestAccAWSAvailabilityZones -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccAWSAvailabilityZones_basic
=== PAUSE TestAccAWSAvailabilityZones_basic
=== RUN   TestAccAWSAvailabilityZones_stateFilter
=== PAUSE TestAccAWSAvailabilityZones_stateFilter
=== CONT  TestAccAWSAvailabilityZones_basic
=== CONT  TestAccAWSAvailabilityZones_stateFilter
--- PASS: TestAccAWSAvailabilityZones_stateFilter (23.93s)
--- PASS: TestAccAWSAvailabilityZones_basic (23.99s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	24.014s

[aeschright]

Hi @hamstah ! Are you still interested in adding this? The auth code has been split out into a separate package so you would need to submit the PR there: https://github.com/hashicorp/aws-sdk-go-base
After that, documentation could be added to the provider.

[aeschright]

Closing this since I haven't heard back and the next step is to open a PR on the AWS SDK Go Base repo.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!