Add deduplication middleware and publisher decorator

[dkotik]

Useful for many projects. If similar messages appear, discards all but the first one in a given time window.

[codecov]

Codecov Report

Attention: Patch coverage is 71.01449% with 40 lines in your changes are missing coverage. Please review.

Project coverage is 66.96%. Comparing base (d20a605) to head (998e7c4).
Report is 3 commits behind head on master.

Files	Patch %	Lines
message/router/middleware/deduplicator.go	71.01%	29 Missing and 11 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #423      +/-   ##
==========================================
- Coverage   76.69%   66.96%   -9.74%     
==========================================
  Files          57       64       +7     
  Lines        3012     4277    +1265     
==========================================
+ Hits         2310     2864     +554     
- Misses        563     1239     +676     
- Partials      139      174      +35     

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[dkotik]

I bumped the coverage to keep Codecov happy.

[dkotik]

@roblaszczak I resolved all the conversations by doing a bit of a re-write to address the core issue: I added the interface ExpiringKeyRepository and flowed everything around that. If somebody implements Redis backend, they can. Perhaps I will later. Requesting re-review.

[roblaszczak]

Thanks @dkotik 🍻