Show new server index state in cabal v2-update

[jneira]

• Hi, it is a minor ui improvement but i hope it will not be very difficult to implemement
• The actual cabal v2-update default output is:

PS D:\dev\ws\haskell\hls> cabal v2-update
Downloading the latest package list from hackage.haskell.org
To revert to previous state run:
    cabal v2-update 'hackage.haskell.org,2020-06-29T21:09:43Z'

• I often need to know the actual timestamp, not the previous one, to fill the index-state cabal.project field or simply compare with release or revisions dates on hackage.
  • So i have to run a second cabal update to make it tell me the last state, just downloaded
• So the output could be changed to something like:

 PS D:\dev\ws\haskell\hls> cabal v2-update
Downloading the latest package list from hackage.haskell.org
hackage.haskell.org index state updated to '2020-06-29T22:09:43Z'
To revert to previous state run:
    cabal v2-update 'hackage.haskell.org,2020-06-29T21:09:43Z'

• for each server updated

[phadej]

 cabal --version
cabal-install version 3.3.0.0
compiled using version 3.3.0.0 of the Cabal library 

% cabal update
Downloading the latest package list from hackage.haskell.org
Updated package list of hackage.haskell.org to the index-state 2020-06-30T06:46:07Z
To revert to previous state run:
    cabal v2-update 'hackage.haskell.org,2020-06-25T09:14:58Z'

Resolved in #6810, Duplicate of #6804