Update the roleAssignment.bicep module principalType property so that warnings do not occur

[glennmusa]

Benefit/Result/Outcome

So that deployments do not present warnings.

Description

Update the roleAssignment module's principalType to reflect the expected values:

Today's implementation:

missionlz/src/bicep/modules/roleAssignment.bicep

Lines 4 to 16 in 6bdbf97

	@allowed([
	'User'
	'Group'
	'ServicePrincipal'
	'Unknown'
	'DirectoryRoleTemplate'
	'ForeignGroup'
	'Application'
	'MSI'
	'DirectoryObjectOrGroup'
	'Everyone'
	])
	param principalType string = 'ServicePrincipal'

The expected values are one of ForeignGroup, Group, ServicePrincipal, User, null as reported by the Bicep warning below:

workspaces/missionlz/src/bicep/modules/roleAssignment.bicep(23,20) : Warning BCP036: The property "principalType" expected a value of type "'ForeignGroup' | 'Group' | 'ServicePrincipal' | 'User' | null" but the provided value is of type "'Application' | 'DirectoryObjectOrGroup' | 'DirectoryRoleTemplate' | 'Everyone' | 'ForeignGroup' | 'Group' | 'MSI' | 'ServicePrincipal' | 'Unknown' | 'User'".

Acceptance Criteria

• Role assignments still occur when necessary for policy, but without warnings at deployment time

[lisamurphy-msft]

Instead of updating the list of allowed types, to include a null value - I think it might make more sense to remove the @Allowed stanza. Preliminary tests of this approach are returning successful - doing some additional testing and gathering peer feedback.