Improve error handling for the SAML login endpoint when the caller is missing a `Content-Type` request header

[robotdan]

Improve error handling for the SAML login endpoint when the caller is missing a Content-Type request header

Description

When the caller omits the Content-Type ideally we want to provide a nice error message.

If you send a request body to /samlv2/login w/out a Content-Type header, or using an un-supported value, the error will not be displayed nicely.

Instead you'll see something ugly in the logs

Error org.primeframework.mvc.PrimeMVCRequestHandler - Error encountered
org.primeframework.mvc.PrimeException: Missing result for action class [class io.fusionauth.app.action.samlv2.LoginAction] URI [/samlv2/login] and result code [input]

Additionally, ignore the binding request parameter if present.

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[robotdan]

Internal:

• https://github.com/FusionAuth/fusionauth-app/pull/425

[andrewpai]

Shipping in 1.51.0