FEATURE - ADP: Prompt for credentials when not available in VSCode

[IvoSG]

As a developer creating an adaptation project,
I want to be prompted for credentials when they're not stored in VSCode,
so that I can authenticate to ABAP systems without pre-configuring credentials

Description

Adds a credential storage prompt that allows users to save ABAP system credentials (username/password) via @sap-ux/store when not already available, streamlining authentication for future project creation.

Technical Design

New Module: src/app/credential-storage.ts - Handles credential storage logic
Enhanced: Added storeCredentials confirmation prompt in configuration questions
Behavior: Prompts after password entry, stores credentials securely if user opts-in (ABAP environments only)

Acceptance Criteria

Given I am creating an ABAP adaptation project
When I provide credentials and opt-in to store them
Then credentials are saved via @sap-ux/store for future use

Given I am creating a CF adaptation project
When the project generation runs
Then credential storage is skipped

Notes

• Opt-in via confirmation prompt (defaults to false)
• ABAP environments only (not CF)
• Updates existing credentials with force flag

Tasks

• Unit Tests added
• Test Cases defined