Adds a configuration flag to create table on save

[imaximix]

I've added a configuration so you can prevent table creation on save.
We manage tables with something else, so we want to avoid it in production.

I saw that there is another PR that also does this here

[codecov]

Codecov Report

Merging #656 (c9574f4) into master (6d757f1) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head c9574f4 differs from pull request most recent head 5cdfcc9. Consider uploading reports for the commit 5cdfcc9 to get more accurate results

@@           Coverage Diff           @@
##           master     #656   +/-   ##
=======================================
  Coverage   90.33%   90.34%           
=======================================
  Files          62       62           
  Lines        3157     3160    +3     
=======================================
+ Hits         2852     2855    +3     
  Misses        305      305           

Impacted Files	Coverage Δ
lib/dynamoid/config.rb	90.32% <100.00%> (+0.15%)	⬆️
lib/dynamoid/persistence.rb	98.18% <100.00%> (+0.02%)	⬆️

[andrykonchin]

Could you please squash commits into a single one after CI passes successfully?

[andrykonchin]

Thank you!