Add S3 settings in WP Config

[junaidbhura]

Is your enhancement related to a problem? Please describe.
Setting S3 settings in the database can be undesirable in many cases, especially when sharing the database with other people.

Another use case is in CI systems, where it would be easier to save data into the environment, and just add that into the settings.

Describe the solution you'd like
It would be great if the settings are able to be defined as PHP constants, like the database config.