REST API: list endpoints at base URL

[ltalirz]

fixes #3916

The base URL of the REST API was returning a 404 invalid URL response
without providing any guidance to new users as to how to use the API.
We change this to return the list of endpoints formerly available only
under /server/endpoints.

Documentation of where to find the list of endpoints -- which seems
to have been entirely deleted -- is reintroduced.

[codecov]

Codecov Report

Merging #4412 into develop will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #4412      +/-   ##
===========================================
+ Coverage    79.29%   79.32%   +0.03%     
===========================================
  Files          475      475              
  Lines        34837    34838       +1     
===========================================
+ Hits         27622    27632      +10     
+ Misses        7215     7206       -9     

Flag	Coverage Δ
#django	73.17% <100.00%> (+0.05%)	⬆️
#sqlalchemy	72.40% <100.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiida/restapi/api.py	76.09% <ø> (ø)
aiida/restapi/resources.py	96.59% <100.00%> (+2.04%)	⬆️
aiida/orm/utils/log.py	76.67% <0.00%> (-16.66%)	⬇️
aiida/engine/daemon/runner.py	79.32% <0.00%> (-3.44%)	⬇️
aiida/engine/daemon/client.py	72.42% <0.00%> (-1.14%)	⬇️
aiida/sphinxext/process.py	95.81% <0.00%> (+0.67%)	⬆️
aiida/orm/nodes/data/list.py	80.25% <0.00%> (+0.98%)	⬆️
aiida/restapi/common/utils.py	74.08% <0.00%> (+2.39%)	⬆️
aiida/sphinxext/calcjob.py	100.00% <0.00%> (+6.67%)	⬆️
... and 1 more

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[ltalirz]

@giovannipizzi @asle85 Does this look good to you?

[elsapassaro]

Thanks @ltalirz ! It looks good to me

[ltalirz]

@giovannipizzi Could you look into reviewing & merging this?

[giovannipizzi]

Thanks a lot @ltalirz !
However as codecov points out, the new code path (line 44) is not tested - could you add a test for the / path? (Probably it could be a copy-paste from one of the existing tests?)

[ltalirz]

Makes sense - added!