fix(teams): use better URL format and nicer output

[piksel]

• Change the URL format (with support for reading the old format) to one that is easier to type by hand
• Add title and color fields
• Use sections for messages (align with common bot output)
• Correctly parse and test webhook URLs
• Add groundwork for rich API

[codecov]

Codecov Report

Merging #117 (8e8fa37) into main (7e4a3bf) will increase coverage by 3.08%.
The diff coverage is 61.90%.

@@            Coverage Diff             @@
##             main     #117      +/-   ##
==========================================
+ Coverage   61.11%   64.19%   +3.08%     
==========================================
  Files          55       55              
  Lines        1237     1296      +59     
==========================================
+ Hits          756      832      +76     
+ Misses        429      397      -32     
- Partials       52       67      +15     

Impacted Files	Coverage Δ
pkg/services/teams/teams_token.go	38.46% <33.33%> (+38.46%)	⬆️
pkg/services/teams/teams_config.go	55.93% <55.76%> (+55.93%)	⬆️
pkg/services/teams/teams.go	76.92% <78.04%> (+55.04%)	⬆️
pkg/router/router.go	66.30% <0.00%> (+5.43%)	⬆️

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