There should be a programmatic way to get the current space guid

What's the user value of this feature request?
Improve scripting capabilities of cf curl ...

Who is the functionality for?
CF users and CI / CD builders

How often will this functionality be used by the user?
It is going to be used in scripts and CI/CDs. It is hard to say how often.

Who else is affected by the change?
Not a breaking change

Is your feature request related to a problem? Please describe.
There is no reliable scriptable way of checking if an application exists in the current space unless:

• we know guid of the current space (GET /v3/apps?names=APPNAME&space_guids=SPACE_GUID)
  OR
• we know guid of the application itself
  OR
• cf app appname produces a parsable response so that there is no need to check for unreliable App 'APPNAME' not found

Describe the solution you'd like
cf target or cf space should have an option to get guid of the current space

Describe alternatives you've considered
Another option would be to parse ~/.cf/config.json though I'm not sure if this file has a stable format and supposed to be read by users. I'd expect this not to be the case.