feature: Support for setting Account Closure and Alternate Contacts

1. Account Closure is now supported through Organizations API:
https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/organizations.html#Organizations.Client.close_account

2. Alternate contacts `'BILLING'|'OPERATIONS'|'SECURITY'` for can be set via:
https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/account.html#Account.Client.put_alternate_contact

No repository files, tests, configuration fields, or entry points are named. Start by tracing the existing account-management flow, then read the linked Organizations close_account and Account put_alternate_contact API documentation. Done should provide account closure support and allow BILLING, OPERATIONS, and SECURITY alternate contacts to be set.

Written by the indexing model from the issue text.