Make IBKRCATEGORY an environment variable for self-hosting

[Trefex]

Summary by Sourcery

This pull request introduces the ability to configure the IBKRCATEGORY via an environment variable (GHOST_IBKR_PLATFORM) for self-hosting setups. It also updates the README with instructions on how to retrieve and set this platform ID.

• Enhancements:
  • Made the IBKRCATEGORY configurable via the GHOST_IBKR_PLATFORM environment variable for self-hosting.
• Documentation:
  • Added instructions to the README for configuring and retrieving the platform ID for self-hosting.

[sourcery-ai[bot]]

Reviewer's Guide by Sourcery

This pull request refactors the code to make the IBKR platform ID configurable via an environment variable, which is particularly useful for self-hosting scenarios. The changes include updates to the README.md to provide setup instructions, modifications to the SyncIBKR class to accept and use the new environment variable, and adjustments in main.py to pass the environment variable to the SyncIBKR class.

File-Level Changes

Files	Changes
SyncIBKR.py main.py	Refactored the code to use an environment variable for the IBKR platform ID instead of a hardcoded value, enhancing configurability for self-hosting.

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