feat: Support for cognito federated indentities

[Rob-Powell]

Issue #, if available:

#387

Description of changes:

Users of the solution usually want to quickly demo and highlight value, connecting to an organisations existing identity provider is a quick way of enabling secure access to the solution to a defined user base.

Adds support for users to configure and leverage the solutions ability to Federate user logon via supported Cognito federation.

I have written docs for this solution see additions under docs/

Currently this solution only supports:

• Cognito custom OIDC providers.
• Cognito custom SAML providers.
• Supports setting the configuration later within the setup process but a helpful guided process is also provided.

2 Custom Resource lambda functions had to be used"

• 1 to update the cognito client with the created domain (circular dependency)
• 2 to securely pass the OIDC client secret to the cognito identity provider avoiding having the secret stored in cloudformation

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