Add the requested vectors of trust to ServiceProviderRequest

[jmhooper]

We are working on imlementing a feature for partners to request identity proofing and authentication features using vectors of trust. This will involve sending param describing the vector of trust in the original SAML or OIDC request. Within the context of OIDC this param is named vtr.

This commit adds a vtr property to ServiceProviderRequest. This property is unused and unset in the persisted service provider request. This will allow us to write to it in the future and initialize ServiceProviderRequests with the value without resulting in an ArgumentError (thus avoiding a dreaded 50/50 state bug)

[zachmargolis]

should we add acr too? so we dont have to persisnt ial//aal separately?

Suggested change

	vtr: nil # rubocop:disable Lint/UnusedMethodArgument
	vtr: nil, # rubocop:disable Lint/UnusedMethodArgument
	acr: nil # rubocop:disable Lint/UnusedMethodArgument

[jmhooper]

I have wavered on whether we should add ACR separately. They get split out and parsed separately by both the OIDC controller and the SAML request.

I was imagining something like this (at least for now):

class ServiceProviderRequest
  def acr_values
    [ial, aal].join(' ')
  end
end

Eventually we may get to a place where we can pass in a raw ACR value. I'm not sure whether that is better to go for now or hold off on. I haven't spent enough time hacking on either the SAML or OIDC portion to know which is better.

[jmhooper]

Okay, I did some poking around and decided to go ahead and throw the raw "acr_values" prop on there