Configurable actor reminder storage patitions

[berndverst]

Description

Adds support for configuring the actor reminder storage partitions

Issue reference

dapr/dapr#2889

Checklist

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

Merging #236 (d92b1a6) into master (1492d89) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #236      +/-   ##
==========================================
+ Coverage   88.53%   88.55%   +0.01%     
==========================================
  Files          52       52              
  Lines        2068     2071       +3     
==========================================
+ Hits         1831     1834       +3     
  Misses        237      237              

Impacted Files	Coverage Δ
dapr/actor/runtime/config.py	100.00% <100.00%> (ø)

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[berndverst]

@wcs1only could you please review this so it lands in the next version of the SDK? This depends on dapr/dapr#3297 which was just merged. The parent issue is dapr/dapr#2889