[CI] Add a debug build configuration

Summary:
This diff adds a standalone debug build configuration that runs the unit
tests, non-extended functional tests and secp256k1 tests. It is flagged
to run on each diff so we can catch the runtime lock assertions early.

Test Plan:

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

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7979