feat: implement "create admin session" capability

[travis]

Implement plan/create-admin-session - see https://github.com/w3s-project/console/pull/98 for an example of this in action.

Originally https://github.com/w3s-project/w3infra/pull/358, moving here to unstick the integration tests.

[seed-deploy[bot]]

View stack outputs

- **pr374-w3infra-BillingDbStack** Name | Value -- | -- customerTableName | pr374-w3infra-customer spaceDiffTableName | pr374-w3infra-space-diff spaceSnapshotTableName | pr374-w3infra-space-snapshot usageTable | pr374-w3infra-usage - **pr374-w3infra-BillingStack** Name | Value -- | -- ApiEndpoint | https://g8sqe0ayve.execute-api.us-east-2.amazonaws.com billingCronHandlerURL | https://iovdtfijmsa5564szlxa65nk640ovtjp.lambda-url.us-east-2.on.aws/ CustomDomain | https://pr374.billing.web3.storage - **pr374-w3infra-CarparkStack** Name | Value -- | -- BucketName | carpark-pr374-0 Region | us-east-2 - **pr374-w3infra-RoundaboutStack** Name | Value -- | -- ApiEndpoint | https://amgvbc77kd.execute-api.us-east-2.amazonaws.com CustomDomain | https://pr374.roundabout.web3.storage - **pr374-w3infra-SatnavStack** Name | Value -- | -- BucketName | satnav-pr374-0 Region | us-east-2 - **pr374-w3infra-UploadApiStack** Name | Value -- | -- ApiEndpoint | https://9juwmnapx4.execute-api.us-east-2.amazonaws.com CustomDomain | https://pr374.up.web3.storage - **pr374-w3infra-BusStack** - **pr374-w3infra-FilecoinStack** - **pr374-w3infra-ReplicatorStack** - **pr374-w3infra-UcanFirehoseStack** - **pr374-w3infra-UcanInvocationStack** - **pr374-w3infra-UploadDbStack**