Add blockquote support for HTML and MD2

[adasauce]

adds support for the blockquote formatting option as documented here: https://core.telegram.org/bots/api#formatting-options

I needed this for my own implementation, figured I would share it upstream.

Thanks for writing this :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (08d77d3) 94.01% compared to head (aedebfc) 94.02%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #138   +/-   ##
=======================================
  Coverage   94.01%   94.02%           
=======================================
  Files          20       20           
  Lines        2056     2058    +2     
=======================================
+ Hits         1933     1935    +2     
  Misses         87       87           
  Partials       36       36           

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