[Bitbucket] Adding filterText REST parameter for Get pull requests for

[thopx14]

I'm missing the REST parameter filterText for get_pull_requestsfunction. I added it and tested it with our companies on-premise bitbucket solution.

Thanks in adavance :-)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 33.64%. Comparing base (7cbbd62) to head (2b4b3dd).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
atlassian/bitbucket/__init__.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1542      +/-   ##
==========================================
- Coverage   33.65%   33.64%   -0.01%     
==========================================
  Files          48       48              
  Lines        9291     9293       +2     
  Branches     1247     1248       +1     
==========================================
  Hits         3127     3127              
- Misses       6041     6043       +2     
  Partials      123      123              

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