Add diag request for Synapse

[bmarty]

Improve the hs_diag script to fetch info about the server version:

For instance, when running ./tools/hs_diag.py -s matrix.org

We will get this extra bloc:

====================================================================================================
# Synapse version (https://matrix.org/_synapse/admin/v1/server_version)
====================================================================================================
{
    "server_version": "1.58.0rc2",
    "python_version": "3.7.3"
}

[github-actions]

Unit Test Results

122 files  ±0  122 suites  ±0   2m 22s ⏱️ +15s
205 tests ±0  205 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
690 runs  ±0  690 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 8e31906. ± Comparison against base commit c9bd1f3.

[onurays]

Nice, LGTM! (I just re-run the lint runner)

[ouchadam]

TIL about this helper 👍

thinking out loud for more features, could also be helpful to grab the homeservers .wellknown and (just seen we're already doing this!) ssl/tls certificates

[bmarty]

Thanks for the review. Any improvement on this helper would be considered :)