notify: create telemetry spans when sending emails, pd, slack

[adamdecaf]

No description provided.

[codecov-commenter]

Codecov Report

Attention: 25 lines in your changes are missing coverage. Please review.

Comparison is base (6dbedc8) 48.91% compared to head (b93349e) 48.97%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #212      +/-   ##
==========================================
+ Coverage   48.91%   48.97%   +0.06%     
==========================================
  Files          87       87              
  Lines        4042     4059      +17     
==========================================
+ Hits         1977     1988      +11     
- Misses       1744     1750       +6     
  Partials      321      321              

Files	Coverage Δ
internal/incoming/stream/publisher.go	66.66% <100.00%> (+2.38%)	⬆️
internal/notify/mock_sender.go	57.14% <100.00%> (ø)
internal/notify/multi.go	53.24% <100.00%> (+0.68%)	⬆️
internal/notify/slack.go	80.39% <100.00%> (+1.66%)	⬆️
internal/notify/email.go	59.57% <60.00%> (+2.27%)	⬆️
internal/notify/kafka.go	0.00% <0.00%> (ø)
internal/pipeline/aggregate.go	49.16% <0.00%> (-0.84%)	⬇️
internal/notify/pagerduty.go	0.00% <0.00%> (ø)

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