[DOP-28371] Add OAuth2 authentication support to Iceberg REST Catalog

[IlyasDevelopment]

Change Summary

• Added IcebergRESTCatalogAuth base class with get_config() method
• Implemented IcebergRESTCatalogOAuth2, IcebergRESTCatalogBearerAuth classes
• Updated IcebergRESTCatalog class to accept auth: IcebergRESTCatalogAuth

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.

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
onetl/connection/db_connection/iceberg
connection.py	193	47	75%	262–264, 381–382, 384–385, 389, 391, 420–422, 424–425, 427–429, 439, 441–442, 458–459, 461–464, 466–468, 470, 491–492, 507–509, 511, 513, 525–528, 535, 537, 539–540, 542, 544
TOTAL	9822	311	96%