[JIFFY-293] Make locale settings configurable in Jiffy

[jama5262]

What does this PR do?

Make locale settings configurable in Jiffy. Such as

1. Make start of week, relative date time and ordinals

Issue Reference

Fixes #293

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Maintenance change (non-breaking change such as upgrading a dependency, refactoring, or making a lint fix)
• Documentation update
• Breaking change (a fix or feature that would cause existing functionality to change)

Screenshots

If applicable, add screenshots to help explain your problem.

Checklist

• Wrote additional tests, if needed
• All tests have passed, you can find the scripts from the ./bin folder
• I have updated the documentation accordingly, if needed.

Additional Information

[codecov]

Codecov Report

Attention: Patch coverage is 93.02326% with 60 lines in your changes missing coverage. Please review.

Project coverage is 95.79%. Comparing base (8a94744) to head (1d50c84).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/src/locale/relative_date_time.dart	91.97%	57 Missing ⚠️
lib/src/global/global_start_of_week.dart	80.00%	2 Missing ⚠️
lib/src/jiffy.dart	97.43%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #294      +/-   ##
==========================================
- Coverage   96.46%   95.79%   -0.67%     
==========================================
  Files          36       15      -21     
  Lines        1611     1452     -159     
==========================================
- Hits         1554     1391     -163     
- Misses         57       61       +4     

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