Migrate the package to use the new `lakefs` SDK wrapper library

[nicholasjng]

Addresses #195.

Progress:

• [x] Migrated LakeFSFileSystem
• [x] Migrated LakeFSFile
• [x] Deleted lakefs_spec.config
• [x] Migrated conftest
• [x] Migrated unit tests
• [x] Migrated smoke tests
• [x] Deleted lakefs_spec.client_helpers
• [x] Migrated LakeFSTransaction

A point of contention is the client initialization. ~I removed the client configuration attributes for now, but they could be added back depending on whether we want to still support them.~ EDIT: The attributes are added back, but the configfile is pending a decision, as stated below.

As for the config file - lakefs currently only supports the default location $HOME/.lakectl.yaml, so if we take over their behavior, the configfile argument is not useful anymore until they allow other files.

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (524eb23) 90.56% compared to head (71bd77d) 91.31%.

Files	Patch %	Lines
src/lakefs_spec/transaction.py	95.91%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #231 +/- ## ========================================== + Coverage 90.56% 91.31% +0.75% ========================================== Files 7 5 -2 Lines 551 472 -79 Branches 93 81 -12 ========================================== - Hits 499 431 -68 + Misses 27 23 -4 + Partials 25 18 -7 ```

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[nicholasjng]

Hahaha, this change deletes so many lines that the new coverage falls below the current total coverage target!