Allow options dict value to be set

[mattgaff]

I was looking for a way to override options and saw it did not exist.

I did not see any movement on this PR: https://github.com/jazzband/dj-database-url/pull/178.

Apologies if its bad etiquette to step in and add this feature when that is open, but it hasn't had any updates in a while.

What's changed:

• config now supports options dictionary.
• parse not supports options dictionary.
  • old options is now query_string_options
  • new options value being used is for the {DATABASES: {'OPTIONS': {}}}
• Added check_if_query_string_options_overlaps_options function to fail if configuration is overlapping.
  • For example, adding sslmode=true to URL, and also adding it to OPTIONS
  • I felt like it would be bad practice to automatically override user values, because we'd need to make a choice as to which value "wins" the query param one (sslmode, currentSchema) or the OPTIONS one.

[codecov[bot]]

Codecov Report

Merging #220 (ed55531) into master (a7f94c8) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #220   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines           69        84   +15     
  Branches        16        19    +3     
=========================================
+ Hits            69        84   +15     

Impacted Files	Coverage Δ
dj_database_url/__init__.py	100.00% <100.00%> (ø)

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