[CMAKE] Generate textual coverage report

Summary:
This will allow the bot to generate remarkup content to be display in a
Phabricator panel.

Test Plan:

./contrib/teamcity/build-configurations.py build-coverage

Check the text report are generated and part of the coverage archive.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7094