Support SQL column with NOT NULL constraint

[rulle-io]

Creates an Avro schema with a field type instead of [null, type] for SQL column with NOT NULL constrain. Configurable behaviour.

Checklist for PR author(s)

• [x] Changes are covered by unit tests (no major decrease in code coverage %) and/or integration tests.
• [x] Ensure code formating (use mvn com.coveo:fmt-maven-plugin:format org.codehaus.mojo:license-maven-plugin:update-file-header)
• [x] Document any relevant additions/changes in the appropriate spot in javadocs/docs/README.

[codecov[bot]]

Codecov Report

Merging #581 (de21f4e) into master (1668c7d) will decrease coverage by 1.32%. The diff coverage is 70.96%.

:exclamation: Current head de21f4e differs from pull request most recent head ef39bed. Consider uploading reports for the commit ef39bed to get more accurate results

@@             Coverage Diff              @@
##             master     #581      +/-   ##
============================================
- Coverage     91.47%   90.16%   -1.32%     
- Complexity      243      255      +12     
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  Files            26       27       +1     
  Lines           927      966      +39     
  Branches         67       66       -1     
============================================
+ Hits            848      871      +23     
- Misses           52       60       +8     
- Partials         27       35       +8