Session init disable on CLI is outdated

Problem/Motivation

Core for sure but also I think Symfony as well stops session init when the current SAPI is CLI. In the age of app servers this is no longer correct.

Steps to reproduce

Run Drupal from roadrunner and try to start a session.

Proposed resolution

Remove these roadblocks, plain and simple.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet