[DOP-6701] Add SparkLocalFS connection

[dolfinus]

Change Summary

• Added SparkLocalFS class and related tests, docs and CI job
• Updated docs structure - moved folders db_connection and file_connection to subfolders of new connection folder, added here file_df_connection subfolder.
• While implementing SparkFileDFConnection._check_if_supported I've found that Greenplum/MongoDB._check_if_driver_imported were called in read_source/write_target methods, but they are useless because this check is already done in .check() method. Removed these calls.

Currently there are no integration tests for reading & writing files because there are no file formats implemented. They will be added in future pull requests.

Related issue number

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[codecov]

Codecov Report

Merging #67 (13f3bbe) into develop (2caf92f) will decrease coverage by 0.33%.
The diff coverage is 81.66%.

@@             Coverage Diff             @@
##           develop      #67      +/-   ##
===========================================
- Coverage    93.15%   92.82%   -0.33%     
===========================================
  Files          133      135       +2     
  Lines         6209     6317     +108     
  Branches      1156     1172      +16     
===========================================
+ Hits          5784     5864      +80     
- Misses         327      350      +23     
- Partials        98      103       +5     

Impacted Files	Coverage Δ
onetl/connection/db_connection/kafka/connection.py	91.48% <0.00%> (ø)
...netl/connection/file_connection/mixins/__init__.py	100.00% <ø> (ø)
...ion/file_df_connection/spark_file_df_connection.py	74.64% <74.64%> (ø)
onetl/connection/__init__.py	90.00% <80.00%> (+3.33%)	⬆️
...tl/connection/file_df_connection/spark_local_fs.py	92.30% <92.30%> (ø)
conftest.py	98.64% <100.00%> (+0.05%)	⬆️
onetl/base/base_connection.py	100.00% <100.00%> (ø)
onetl/connection/db_connection/greenplum.py	69.33% <100.00%> (-0.29%)	⬇️
onetl/connection/db_connection/jdbc_mixin.py	95.05% <100.00%> (ø)
onetl/connection/db_connection/mongodb.py	94.00% <100.00%> (-0.09%)	⬇️

... and 2 files with indirect coverage changes