Added prometheus metrics middleware.

[s3rius]

This PR adds middleware that enables prometheus compatible metrics.

[codecov-commenter]

Codecov Report

Merging #99 (2d94ee9) into develop (e66f3aa) will decrease coverage by 2.87%.
The diff coverage is 47.42%.

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@@             Coverage Diff             @@
##           develop      #99      +/-   ##
===========================================
- Coverage    67.62%   64.75%   -2.87%     
===========================================
  Files           37       39       +2     
  Lines          942     1013      +71     
===========================================
+ Hits           637      656      +19     
- Misses         305      357      +52     

Impacted Files	Coverage Δ
taskiq/cli/watcher.py	0.00% <ø> (ø)
taskiq/cli/worker/run.py	0.00% <0.00%> (ø)
taskiq/formatters/json_formatter.py	100.00% <ø> (ø)
taskiq/receiver/params_parser.py	96.87% <ø> (ø)
taskiq/utils.py	72.72% <25.00%> (-27.28%)	⬇️
taskiq/middlewares/prometheus_middleware.py	27.77% <27.77%> (ø)
taskiq/receiver/receiver.py	86.59% <87.50%> (ø)
taskiq/__init__.py	100.00% <100.00%> (ø)
taskiq/abc/broker.py	85.39% <100.00%> (ø)
taskiq/brokers/inmemory_broker.py	96.61% <100.00%> (+0.11%)	⬆️
... and 5 more

... and 1 file with indirect coverage changes

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