🧪 Add test for needreport directive

[chrisjsewell]

Currently there is no test for this directive, this PR adds one.

This PR also fixes the directive:

• Make the options flags
• Change errors in the directive to emit warnings, rather than excepting the whole build
• Allow for template to be specified as a directive option
• Allow the the dropdown directive used in the default template, which requires an external sphinx extension, to be overriden using needs_render_context = {"report_directive": "admonition"} (I left the default as dropdown, so as not to introduce a breaking change)

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (73b961e) 83.19% compared to head (418f209) 83.86%.

Files	Patch %	Lines
sphinx_needs/directives/needreport.py	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1105      +/-   ##
==========================================
+ Coverage   83.19%   83.86%   +0.66%     
==========================================
  Files          56       56              
  Lines        6456     6438      -18     
==========================================
+ Hits         5371     5399      +28     
+ Misses       1085     1039      -46     

Flag	Coverage Δ
pytests	83.86% <93.33%> (+0.66%)	⬆️

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[chrisjsewell]

I've also just realised there is a bug in this directive:
The usage flag creates a count of user defined need types.
However, it does this during the processing of the directive, rather than in a post-processing step.
Therefore, the count will usually be incorrect.

[danwos]

THanks for the PR and the fixes 👍