chore: apply license headers to all the source files

[feng-tao]

Summary of Changes

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Tests

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Documentation

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CheckList

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• PR title addresses the issue accurately and concisely. Example: "Updates the version of Flask to v1.0.2"
  • In case you are adding a dependency, check if the license complies with the ASF 3rd Party License Policy.
• PR includes a summary of changes.
• PR adds unit tests, updates existing unit tests, OR documents why no test additions or modifications are needed.
• In case of new functionality, my PR adds documentation that describes how to use it.
  • All the public functions and the classes in the PR contain docstrings that explain what it does
• PR passes make test

[codecov-commenter]

Codecov Report

Merging #153 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #153   +/-   ##
=======================================
  Coverage   73.25%   73.25%           
=======================================
  Files          26       26           
  Lines        1249     1249           
  Branches      132      132           
=======================================
  Hits          915      915           
  Misses        307      307           
  Partials       27       27           

Impacted Files	Coverage Δ
metadata_service/api/column.py	100.00% <ø> (ø)
metadata_service/api/dashboard.py	73.33% <ø> (ø)
metadata_service/api/popular_tables.py	100.00% <ø> (ø)
metadata_service/api/system.py	66.66% <ø> (ø)
metadata_service/api/table.py	100.00% <ø> (ø)
metadata_service/api/tag.py	92.85% <ø> (ø)
metadata_service/api/user.py	100.00% <ø> (ø)
metadata_service/config.py	100.00% <ø> (ø)
metadata_service/entity/dashboard_detail.py	100.00% <ø> (ø)
metadata_service/entity/dashboard_query.py	100.00% <ø> (ø)
... and 16 more

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