Update self-hosted Kubernetes deployments examples for compatibility and consistency

[tetuyoko]

This PR updates the Kubernetes deployment configurations (api.yaml, worker.yaml, playwright-service.yaml, configmap.yaml, and README.md) to address compatibility issues and improve consistency with the current Firecrawl application.

Key changes include:

• Apple Silicon Compatibility: Added the --platform linux/amd64 flag to the Docker build commands to ensure compatibility when building on Apple Silicon Macs. This fixes potential runtime issues due to architecture mismatches.
• Missing Environment Variables: Added the FLY_PROCESS_GROUP environment variable to api.yaml and worker.yaml for proper process group identification in Fly.io.
• Corrected Playwright URL: Fixed the PLAYWRIGHT_MICROSERVICE_URL in configmap.yaml to point to the correct service endpoint, resolving communication issues with the Playwright microservice.
• Secret Reference: Added a reference to the firecrawl-secret Secret in the worker deployment to ensure the required OPENAI_API_KEY is available before the worker starts.

These updates ensure the Kubernetes deployments are correctly configured and function as expected in various environments.

[mogery]

Thank you!