editoast: add telemetry on database requests

[woshilapin]

The second commit tries to add identifiers in metadata of the traces. However, it seems that it would be not trivial to do it without the valuable feature... which is unstable.

⚠️ Weirdly, the build with Docker seems to ignore the configuration .cargo/config.toml (hence the build is failing). Needs some investigation if we want to go that path.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.49%. Comparing base (f88f40d) to head (ff1e7dd).
Report is 5 commits behind head on dev.

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Additional details and impacted files

@@              Coverage Diff              @@
##                dev    #7389       +/-   ##
=============================================
+ Coverage     29.44%   87.49%   +58.04%     
=============================================
  Files          1162       31     -1131     
  Lines        143499     1535   -141964     
  Branches       2808        0     -2808     
=============================================
- Hits          42253     1343    -40910     
+ Misses        99588      192    -99396     
+ Partials       1658        0     -1658     

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railjson_generator	87.49% <ø> (ø)
tests	?

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[leovalais]

Nice! I'm not against using the unstable feature as even if that becomes a problem, reverting that single commit wouldn't be much work and won't degrade the service. But I'm wondering whether we should be using Valuable at all as Debug seems to be fine (albeit less readable). And even if we were to parse the span metadata with some script in the future, we can always deserialize it as RON.

Maybe model-X would be a better span name than database-X (an object may require several model operations to be considered "retrieved" from the database, eg. scenarios that also fetch their study and project).

Now that List and Count are merged they also need to be annotated ;)

[woshilapin]

I removed the unstable feature and went Debug everywhere. Looks much better now.

[flomonster]

LGTM! (tested + reviewed)

[leovalais]

Looks great! Since @flomonster already tested it I'll just play with it later ;)