feat: allow env-var based email config

[revolunet]

Fixes Kinto/kinto-emailer#233

Hi, i'm not sure this is the way to fix it, but this allow to use environment variables to configure pyramid email settings

I can now use these variables without any ini file :

MAIL_DEFAULT_SENDER=toto@toto.com
MAIL_HOST=smtp.orange.fr
MAIL_PORT=25

• Add documentation.
• Add tests.
• Add a changelog entry.
• Add your name in the contributors file.
• If you changed the HTTP API, update the API_VERSION constant and add an API changelog entry in the docs
• If you added a new configuration setting, update the kinto.tpl file with it.

[leplatrem]

This is one way of solving it, but I think it would be better to introduce a sort of registry to be used by plugins.

kinto-emailer could register expected settings:

config.kinto_setting("mail.host", default="localhost")
config.kinto_setting("mail.port", cast=int, default=25)
config.kinto_setting("mail.password", env="PASSWD")

See #1544

[revolunet]

i have no idea how to do this :) is there any plugin as example ?

[leplatrem]

I wrote some details here #1544 (comment)

[leplatrem]

Let's discuss there ;)

[leplatrem]

Please reopen if you still would like to see this implemented :)