Make port assignment configurable

[teald]

Adds port_number as a valid option in the interactive configuration option in .dragonsrc. E.g.,

[interactive]
port_number = 8203

The default is the same as it was before (5006).

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 64.21%. Comparing base (eefdd3c) to head (f60b947). Report is 5 commits behind head on master.

Files	Patch %	Lines
geminidr/interactive/interactive_config.py	0.00%	5 Missing :warning:
geminidr/interactive/server.py	0.00%	4 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #459      +/-   ##
==========================================
- Coverage   64.22%   64.21%   -0.02%     
==========================================
  Files         292      292              
  Lines       36665    36673       +8     
==========================================
  Hits        23549    23549              
- Misses      13116    13124       +8     

Flag	Coverage Δ
f2	24.64% <0.00%> (-0.01%)	:arrow_down:
ghost	27.50% <0.00%> (-0.01%)	:arrow_down:
gmosls	36.05% <0.00%> (-0.01%)	:arrow_down:
gnirs	24.92% <0.00%> (-0.01%)	:arrow_down:
gsaoi	17.09% <0.00%> (-0.01%)	:arrow_down:
integration	33.60% <0.00%> (-0.01%)	:arrow_down:
niri	25.25% <0.00%> (-0.01%)	:arrow_down:
regression	31.97% <0.00%> (-0.01%)	:arrow_down:
slow	48.17% <0.00%> (-0.02%)	:arrow_down:
unit	47.77% <0.00%> (-0.02%)	:arrow_down:
wavecal	24.71% <0.00%> (-0.01%)	:arrow_down:

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