Add storage examples for databases and s3

[tibrk]

Related to https://github.com/prokube/prokube-images/pull/56

This pull request add examples for accessing object storage and relational databases from prokube labs, including both Python and RStudio environments. It introduces a new storage directory with organized subfolders for S3 and database access, each containing clear, ready-to-run examples.

New storage examples and documentation:

• Added the storage directory with subfolders for S3 object storage and database access examples, including a high-level README.md describing their structure and usage. [1] [2]
• Updated the main README.md to reference the new storage examples and clarify how to find and use them.

S3 object storage examples:

• Added Python (python/s3_access.ipynb) and R (r/s3_access.R) examples for reading and writing data to S3-compatible object storage, with documentation in storage/s3/README.md. [1] [2] [3]

Relational database access examples:

• Added Python notebooks for PostgreSQL, MariaDB/MySQL, and Microsoft SQL Server, each demonstrating connection, data writing, and reading using both high-level (SQLAlchemy) and low-level (driver/cursor) approaches. [1] [2] [3]
• Added R scripts for PostgreSQL, MariaDB/MySQL, and Microsoft SQL Server, using the DBI and odbc packages, with instructions for credential input and connection setup. [1] [2] [3]
• Included a detailed README.md in storage/database-access explaining the examples, required drivers, and connection setup.