feat: add port and path configurability

[dbschmigelski]

This PR adds environment variable configuration options to enable more flexible deployments of the CopilotKit + Strands starter template.

Changes

Added support for AGENT_PATH, AGENT_PORT, STRANDS_AGENT_URL, and STRANDS_AGENT_BEARER_TOKEN environment variables. The bearer token authentication conditionally includes Authorization header when provided.

Why

This enables more configurable deployments by allowing users to deploy agents on custom ports and paths, use external agent services with authentication without needing to modify the source.

Configuration Example

export AGENT_PATH="./my-custom-agent"
export AGENT_PORT="9000"
export STRANDS_AGENT_URL="http://localhost:9000"
export STRANDS_AGENT_BEARER_TOKEN="your-bearer-token-here"

This change alongside ag-ui-protocol/ag-ui#793 will allow for a quick getting started experience for running AG-UI + Strands on Bedrock AgentCore strands-agents/docs#364

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Testing was done by overriding the ag_ui_strands import with

    "ag_ui_strands @ git+https://github.com/dbschmigelski/ag-ui.git@feat/ping-create-strands-app#subdirectory=integrations/aws-strands/python",