Make deprecation trials more obvious on the feature details page

[past]

A new feature can sometimes have both a deprecation trial and a regular trial. Creating a new OT stage currently doesn't distinguish between regular and deprecation trials until the point when the I2E has been approved and the author tries to request a trial. If we move the input field to the OT stage form we would be able to both distinguish reverse from regular OTs in the feature details (providing better naming guidance in help text too), and also simplify the OT creation form (ot_creation_request) by e.g. not showing the web counter field at all.

In order to better distinguish regular and reverse OTs we could start by changing the stage label (Deprecation Trial/Origin Trial) and consider perhaps adding a "deprecation" chip before the OT stage name.

[past]

Another argument in favor of automatic marking/badging the stage is that feature authors often don't provide a name for the stage (example) leaving readers confused about the feature being both shipping and in OT.