Config from env vars must be normalized

[avdata99]

CONFIG_FROM_ENV_VARS takes precedence over config file and extensions but those settings are not normalized

This is a work in progress.
Is this a bug? Am I missing something?

Features:

• includes tests covering changes
• includes updated documentation
• includes user-visible changes
• includes API changes
• includes bugfix for possible backport

Please [X] all the boxes above that apply

[avdata99]

Just a single test function from the test file updated in this PR is running 🙃

[smotornyuk]

Example of normalizing a single option:

from ckan.common import config_declaration as cd

# get the Option object that contains normalization rules
option = cd['ckan.devserver.port']

# normalize value
assert option.normalize('5000') == 5000

# note: invalid values are not normalized and 
# do not produce any errors in this way
assert option.normalize('sf') == 'sf' 

[avdata99]

I think this is ready for review @smotornyuk

[avdata99]

We decided in the tech meeting to stop giving precedente to CONFIG_FROM_ENV_VARS.
I am going to move the reading of the environment variables earlier in the function so that they are read first and normalized automatically.

[smotornyuk]

@avdata99, would you happen to have time to update this PR on Monday? We will make a patch release soon, and it would be nice to include this fix. If not, I'll add a couple of commits to your PR.

[avdata99]

@smotornyuk, sorry. No, I can't update this PR today. Please feel free to update the branch

[smotornyuk]

Done