[v2] Add ability to set properties in subsections

[kdaily]

This change adds new parameters to the aws configure set command to specify a sub-section for setting a property. These parameters are analogous to the existing --profile parameter. A parameter will be added for each sub-section type and take a value of the subsection name. Following is the generic pattern for the aws configure set command:

aws configure set
  --<sub-section-type> <sub-section-name> \
  <property> <value>

For example, the following command should set the property sso_region to the value us-west-2 in the sso-session sub-section named my-sso-session:

aws configure set
  --sso-session my-sso-session \
  sso_region us-west-2

Following is an example setting a nested property in a sub-section:

aws configure set \
  --<sub-section-type> <sub-section-name> \
  <nested-section>.<property> value

The only sub-section types allowed are services and sso-session.

Issue #, if available:

Description of changes:

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[kdaily]

Usually, mutually exclusive parameter validation is done through an event handler. Example:

aws-cli/awscli/customizations/cloudfront.py

Lines 35 to 38 in 9fcb197

	event_handler.register(
	'operation-args-parsed.cloudfront.create-invalidation',
	validate_mutually_exclusive_handler(['invalidation_batch'], ['paths']),
	)

This uses the operation-args-parsed event in clidriver.ServiceOperation:

aws-cli/awscli/clidriver.py

Line 849 in 9fcb197

event = f'operation-args-parsed.{self._parent_name}.{self._name}'

However, the classes here do not have an event registered anywhere near where parameter arg-parsing is performed. We could register a new event, if its thought that this is too deep in the stack for performing this check. This is where it would need to go:

aws-cli/awscli/customizations/commands.py

Line 158 in 9fcb197

[kdaily]

Initially, I had proposed that mutual exclusivity also account for --profile. Unfortunately, profile resolution happens before, and we've lost any context of where the user set the profile.