New API to allow uploaded files to pass through backend service

[dayland]

This pull request includes several changes to the app/backend/app.py file and minor changes to NOTICE.md and app/backend/testsuite.py. The changes mainly focus on code refactoring, improving readability, and adding new functionality for file uploads.

Code Refactoring and Readability Improvements:

• Consistent Naming Convention: Updated variable names to use uppercase for constants, such as DF_FINAL instead of dffinal, and MODEL_NAME instead of model_name. ([[1]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6L117-R118), [[2]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6R163-R167), [[3]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6L176-R194), [[4]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6L702-R695))
• Import Statements: Organized import statements by adding missing imports and removing duplicates. ([[1]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6R6-R15), [[2]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-d78e1bb3c937516751e3aa92744f9ecc8a4a8ce24c2e5954069fbe1351eda017R9))
• Line Breaks and Indentation: Improved readability by adding line breaks and proper indentation, especially in long function calls and conditions. ([[1]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6L135-R140), [[2]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6L319-L354), [[3]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6L381-R370))

New Functionality:

• File Upload Endpoint: Added a new endpoint to upload files to Azure Blob Storage with metadata tags. ([app/backend/app.pyR848-R878](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6R848-R878))

Minor Changes:

• Documentation: Added docstrings to several functions and classes for better understanding. ([app/backend/app.pyR109](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6R109))
• Removed Redundant Code: Removed unused code and comments to clean up the codebase. ([[1]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6L258-R264), [[2]](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-5f1d71f916fd982ef5a7ab0b78e419d64d02a77c7422911db11911a74f3a8ee6L742-R737))
• NOTICE.md Update: Removed an outdated reference to @azure/storage-blob. ([NOTICE.mdL116-L119](https://github.com/microsoft/PubSec-Info-Assistant/pull/839/files#diff-53337bf7ea91d782c573ac8653c18f95b7b23c38da9de08288639bcec9993406L116-L119))

These changes collectively aim to enhance the maintainability, readability, and functionality of the codebase.