refactor(observability): avoid panics caused by missing labels

[Reasno]

No description provided.

[codecov]

Codecov Report

Merging #213 (5c066c0) into master (60953bf) will decrease coverage by 0.14%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master     #213      +/-   ##
==========================================
- Coverage   82.39%   82.25%   -0.15%     
==========================================
  Files          92       92              
  Lines        3465     3494      +29     
==========================================
+ Hits         2855     2874      +19     
- Misses        455      460       +5     
- Partials      155      160       +5     

Impacted Files	Coverage Δ
observability/observability.go	100.00% <ø> (ø)
otkafka/reader_metrics.go	97.53% <33.33%> (-2.47%)	⬇️
otkafka/writer_metrics.go	95.40% <33.33%> (-2.25%)	⬇️
srvgrpc/metrics.go	77.41% <60.00%> (-18.24%)	⬇️
observability/metrics.go	100.00% <100.00%> (ø)
otgorm/gorm_metrics.go	100.00% <100.00%> (ø)
otredis/metrics.go	100.00% <100.00%> (ø)
srvhttp/metrics.go	84.61% <100.00%> (+0.83%)	⬆️

---

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 60953bf...5c066c0. Read the comment docs.