Implement Server Timing performance metrics

Problem/Motivation

Providing server timing would help developers estimate site performance.
The corresponding W3C specification is currently in "Working Draft" status and its already supported by Google Chrome and Firefox.
https://www.w3.org/TR/server-timing/
Symfony adopted it in https://github.com/symfony/symfony/pull/27985

Proposed resolution

Add Server-Timing header with relevant timing information.

Remaining tasks

Decide how enable the Server-Timing.

Proposals

1. Add it to develoment.services.yml (#2)
2. Enable it be default, for example by adding it to core.services.yml (#7)
3. Create a new module for it (#24)
4. Toggle it via service parameter (#27)
5. Toggle it via configuration option (#38)