Feature/simplified seedkit deployment

[chamcca]

Issue #, if available: #20

Description of changes: Simplify checking for and deploying the Seedkit for consumers.

Enables checking for existence of the seedkit as well as returning the stack_name and stack_outputs if it is deployed:

from aws_codeseeder import commands

deployed, stack_name, stack_outputs = commands.seedkit_deployed(seedkit_name="some-name")

if not deployed:
    commands.deploy_seedkit(seedkit_name="some-name")

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