Support STS session Token

[krisiye]

Type: Enhancement

Is your feature request related to a problem? Please describe. spring cloud aws does not support session token for the credentials manager. This will be useful to add for aws integrations using STS.

Describe the solution you'd like

• Add support under org.springframework.cloud.aws.autoconfigure.context.properties.AwsCredentialsProperties for cloud.aws.credentials.sessionToken
• Add support under org.springframework.cloud.aws.autoconfigure.context.ContextCredentialsAutoConfiguration for sessionToken to be provided to the credentials manager.
• Support STS token rotation with spring cloud vault. (See issue linked below) Necessary bean's holding creds will need to be rebound/refreshed to pick up new accesskey, secretKey and sessionToken.

Describe alternatives you've considered NA

Additional context Related issue for vault: https://github.com/spring-cloud/spring-cloud-vault/issues/572

[krisiye]

Closing in favor of https://github.com/awspring/spring-cloud-aws/issues/73