Jira: add get_custom_field_options method, get_autocomplete_data method, and get_autocomplete_suggestion method.

[jerubball]

Added 3 methods, all relating to custom field options.

get_custom_field_options() method lists possible options for a custom field in a project's context (field configuration).
get_autocomplete_data() method lists field names for JQL suggestion.
get_autocomplete_suggestion() method lists possible auto complete option for JQL suggestion with given field and optional value.

[codecov]

Codecov Report

❌ Patch coverage is 10.52632% with 34 lines in your changes missing coverage. Please review.
✅ Project coverage is 42.23%. Comparing base (766fc16) to head (dc41ea4).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
atlassian/jira.py	8.10%	34 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1609      +/-   ##
==========================================
- Coverage   42.23%   42.23%   -0.01%     
==========================================
  Files          66       66              
  Lines        8595     8664      +69     
  Branches     1038     1057      +19     
==========================================
+ Hits         3630     3659      +29     
- Misses       4825     4862      +37     
- Partials      140      143       +3     

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