New Lab: How to perform actions in sub-accounts which require the root user

[s0enke]

Some things in AWS require the usage of the root user, e.g. changing support plans, or closing the account, or setting MFA.
To login into sub-accounts, one needs to do the password-reset procedure, and with superwerker also the indirection via SSM parameter store to obtain the pw reset url.

TODO:

• Document this in a lab named "Perform root-user actions in sub-accounts"