migrate fully to cf v3 api only

[metskem]

cf_exporter currently uses the cf v2 api to get the app and space summary. For example here.

The cf v2 api has been deprecated for quite some time , but now concrete steps have been proposed to disable it.
Since v3 does not offer an alternative for v2's space and app summary, it will be a challenge to get a solution that does not hammer the Cloud Controller too much.

[benjaminguttmann-avtq]

Hi @metskem ,

I think as a first step we will add a flag that by default disables those calls, so we do not run into issues when it gets disabled in cf-deployment by default.
Next step we want to check if we can replace it with something based on v3.

[gmllt]

I've started to look at bbs in this PR #129 , but unfortunately, I haven't had much time to work on that in recent months.

the principle is to use information from bss to retrieve information on the number of requested instances and the number of running instances