Created an example for 'Get file contents' functionality

[b-l-u-e]

Description:
This PR adds a get-file-contents example to demonstrate how to retrieve file contents using the Hedera JavaScript SDK. This functionality is important for developers who need to access and work with file data stored on the Hedera network.

• Add get-file-contents.js example file
• Implement file contents query using FileContentsQuery
• Include error handling and logging for better developer experience
• Demonstrate proper use of ECDSA keys with the SDK

Related issue(s):

Fixes # 2513

Notes for reviewer:
The example demonstrates:

• Setting up the Hedera client with proper operator credentials
• Querying file contents using FileContentsQuery
• Handling potential errors during the query process
• Logging steps and results for clarity

Please pay special attention to the error handling section, as it's been designed to provide comprehensive information for debugging.

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)
• Follows SDK best practices
• Example runs successfully against testnet

[sonarcloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud