Mapping suggestions

[Anish9901]

Fixes #1820

This PR introduces a /mapper endpoint which returns the suggestions for column mappings in the form of column indices.

Technical details

This can handle discrepancies in column names like:

• Perfect names but in a different order
• Case mismatch
• Column names containing underscores instead of spaces
• Mixture of the above

An exception is raised when no mappings are found and are reflected in the API.

After mappings are found they are validated to ensure that the type of the temp table columns can be type casted to that of the type of target table columns if they differ in data types.

Checklist

• [x] My pull request has a descriptive title (not a vague title like Update index.md).
• [x] My pull request targets the master branch of the repository
• [x] My commit messages follow best practices.
• [x] My code follows the established code style of the repository.
• [ ] I added tests for the changes I made (if applicable).
• [ ] I added or updated documentation (if applicable).
• [x] I tried running the project locally and verified that there are no visible errors.

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[codecov-commenter]

Codecov Report

Base: 92.60% // Head: 92.44% // Decreases project coverage by -0.15% :warning:

Coverage data is based on head (16358f4) compared to base (bf2693a). Patch coverage: 45.83% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1698      +/-   ##
==========================================
- Coverage   92.60%   92.44%   -0.16%     
==========================================
  Files         146      146              
  Lines        7099     7122      +23     
==========================================
+ Hits         6574     6584      +10     
- Misses        525      538      +13     

Flag	Coverage Δ
pytest-backend	92.44% <45.83%> (-0.16%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mathesar/models/base.py	92.87% <25.00%> (-1.20%)	:arrow_down:
mathesar/api/db/viewsets/tables.py	70.14% <33.33%> (-2.87%)	:arrow_down:
...r/api/exceptions/database_exceptions/exceptions.py	89.81% <75.00%> (-0.57%)	:arrow_down:
db/columns/exceptions.py	100.00% <100.00%> (ø)
mathesar/api/exceptions/error_codes.py	100.00% <100.00%> (ø)

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