Moving from an Ultimate floating license to an Ultimate named license is awkward

Bug Description:
If you already have an enterprise.server.url configured, you will never see the dialog that asks you to provide a license file on Ultimate. It will just happily connect and check out a floating license. We now have some customers that have a mix of named and floating Ultimate licenses using an Enterprise server and this is surprising and kinda awkward.

There is a File -> Reset License... that just deletes the license.dat from your home folder and restarts (which triggers the appropriate dialog, if enterprise.server.url is not set), but that isn't helpful for this scenario. Could/should possibly be repurposed for this case as well, though.

There are two workarounds for this, currently:

1. On the initial dialog where you log in to get an "Until I Quit" floating license, edit the Enterprise server URL and remove it, then restart. This will cause the dialog to open.
2. Check in your license and quit Binary Ninja. Then, manually place your license file in license.dat in the Binary Ninja user directory. Then, restart. Binary Ninja will use the named license and not check out a new floating license.

Start by tracing the Ultimate license selection flow around enterprise.server.url, the File → Reset License action, and license.dat handling. Reproduce the case with both named and floating licenses configured through an Enterprise server. Done means users can move to a named license without manually removing the server URL or placing license.dat themselves.