Fix/env vars expect lower case letters

[sinadarbouy]

Ticket(s)

close #583

Description

This PR addresses an issue with the loadEnvVars() function where environment variables were being incorrectly processed due to the strings.ToLower function, which assumed all keys were in lowercase. Configuration blocks, however, use camel case (e.g., activeWrites), causing a mismatch.

• Implemented Key Conversion:
  • Added a new method, ConvertKeysToLowercase, which converts all keys in the global configuration to lowercase during the loading process, ensuring consistency.
• Updated Configuration Files:
  • Modified the configuration files (gatewayd.yaml, gatewayd_tls.yaml, missing_keys.yaml) to use lowercase keys (e.g., active-writes instead of writes).
• Validation Enhancements:
  • Enhanced the ValidateGlobalConfig method to ensure that all keys are lowercase.

Found a bug when errors append into []*gerr.GatewayDError

Previously, the code used a single instance of GatewayDError for all errors. This led to incorrect error messages because the same GatewayDError instance was being modified and appended to the slice, resulting in all errors appearing as if they had the same OriginalError.

Development Checklist

• I have added a descriptive title to this PR.
• I have squashed related commits together.
• I have rebased my branch on top of the latest main branch.
• I have performed a self-review of my own code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added docstring(s) to my code.
• I have made corresponding changes to the documentation (docs).
• I have updated docs using make gen-docs command.
• I have added tests for my changes.
• I have signed all the commits.

Legal Checklist

• I have read the CONTRIBUTING document.
• I have read and understood the Code of Conduct.
• I have read and agreed to the Apache CLA (required).
• I have read and agreed to the LICENSE (required).

[sinadarbouy]

• Test cases still left:
  • Test cases for new functions
  • Test cases for environment variable overwrite values in nested maps