add general basic tests for services

[piksel]

this should bump up the test coverage a bit and fix some smaller serialization issues found while testing.

also, this disables the XMPP service (behind a build constraint) until it's deemed stable.

[codecov]

Codecov Report

Merging #192 (f109c90) into main (603fafc) will increase coverage by 3.20%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #192      +/-   ##
==========================================
+ Coverage   71.15%   74.35%   +3.20%     
==========================================
  Files          88       86       -2     
  Lines        2780     2722      -58     
==========================================
+ Hits         1978     2024      +46     
+ Misses        621      511     -110     
- Partials      181      187       +6     

Impacted Files	Coverage Δ
pkg/router/servicemap.go	100.00% <100.00%> (ø)
pkg/services/mattermost/mattermost_config.go	91.66% <100.00%> (+41.66%)	⬆️
pkg/services/googlechat/googlechat_config.go	81.81% <0.00%> (+45.45%)	⬆️
pkg/services/googlechat/googlechat.go	77.77% <0.00%> (+48.14%)	⬆️
pkg/services/mattermost/mattermost.go	60.00% <0.00%> (+53.33%)	⬆️
pkg/services/join/join.go	69.23% <0.00%> (+69.23%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 603fafc...f109c90. Read the comment docs.