cli: add new command to show user quota usage

[diegodelemos]

With the outcome of https://github.com/reanahub/reana-server/issues/279, we should create a new command to display quota usage for the logged-in user.

$ reana-client quota-show # or similar
...

To take inspiration from similar command-line tools, taking advantage of Click colors to show numbers in a more user-friendly way.

[tiborsimko]

Musings about quota commands:

• We need to show the user the actual "occupancy", i.e. how much of the quota is used.

• We probably won't need to "ask for quota increase" functionality in the CLI.

So we could start with just one-two command in a new section at the end of reana-client --help.

Some options:

(1) Several commands primarily split by action (showing limits/usage, setting limit), for example:

$ reana-client quota-show --resource cpu --report limit
1234 minutes per month
$ reana-client quota-show --resource disk --report limit 
123456 KiB
$ reana-client quota-show --resource disk --report usage
123 KiB
$ reana-client quota-show --resource disk 
123 KiB out of 123456 KiB used (12.34%)

(2) Several commands primarily split by resource (cpu, disk); for example:

$ reana-client quota-cpu --report limit
$ reana-client quota-disk --report usage

By analogy with secrets-* I guess we can go for (1) which will open future possibilities of quota-set (some resource), quota-get (some resource), quota-list (gimme all resources that are under quota management), etc.

$ reana-client quota-list --resources
cpu
disk
$ reana-client quota-show --resource disk
123 KiB out of 123456 KiB used (12.34%)