Provide hints when an invalid license id is input

[JJJollyjim]

• Added tests for changed code.
• [n/a?] Updated documentation for changed code.

Currently, the poetry new/init license field can be a little opaque to new users -- here is the actual output from my first time using poetry a few hours ago:

This command will guide you through creating your pyproject.toml config.

Package name [projects]: attoate  
Version [0.1.0]: 
Description []: 
Author [Jamie McClymont <jamie@kwiius.com>, n to skip]: 
License []: GPLv3+ 
 Invalid license id: GPLv3+ 
License []: help
 Invalid license id: help 
License []: ?
 Invalid license id: ? 
License []: gpl-3-or-later
 Invalid license id: gpl-3-or-later 
License []: ?
 Invalid license id: ? 

-------- Some googling later --------

License []: GPL-3.0-or-later

This PR improves the error message to show a link to the SPDX license list, and in common cases, a best-effort guess at which license ids you might be looking for. For example:

invalid license id: some-wacky-license
Poetry uses SPDX license identifiers: https://spdx.org/licenses/

Or, if a common license id is recognised:

Invalid license id: that one from the apache web server
Poetry uses SPDX license identifiers: https://spdx.org/licenses/
Did you mean one of the following?
 * Apache-1.0
 * Apache-1.1
 * Apache-2.0

I'm not a python dev (as evidenced by the fact I didn't know what a license id was :P), feedback is welcome :)

[finswimmer]

Hello @JJJollyjim ,

thanks a lot for this improvement of the user experience. I really like it!

I think it is ok if we integrate it into the master branch. Could your rebase your commit on that branch?

fin swimmer

[JJJollyjim]

Done, I believe :)

[finswimmer]

Perfect!

[JJJollyjim]

Anything else I can do on this?

[brechtm]

This message is just a friendly reminder, since this PR seems ready to be included.

[finswimmer]

@JJJollyjim may I ask you to add a minor change and push again, so that the checks will run again? Afterwards I will be able to merge it.

[finswimmer]

Great. Thanks a lot 👍

change is included