[FEATURE] Add --session-duration option to let user choose how many time last STS temporary credentials

[benjamin-brabant]

Is your feature request related to a problem? Please describe.
Currently we cannot ask awscli_saml_sso for a custom session-duration of generated STS temporary credentials.
We propose to add a --session-duration option to let user choose custom session duration.

Describe the solution you'd like
Add a --session-duration option which let user choose duration in seconds.

We have to ensure that provided value is between 900 (15 min) and 43200 (12 hours).
https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/sts.html#STS.Client.assume_role_with_saml

We also need to handle case when chosen value exceed the MaxSessionDuration set for the role which raised the following exception:

botocore.exceptions.ClientError: An error occurred (ValidationError) when calling the AssumeRoleWithSAML operation: The requested DurationSeconds exceeds the MaxSessionDuration set for this role.

see: https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_use.html#id_roles_use_view-role-max-session