Multiple gateway fixes

[mkysel]

Fix gateway configuration and initialization by renaming binary to xmtpd-gateway, adding development script, and updating component startup

• Renames the gateway binary from xmtpd to xmtpd-gateway in dev/docker/gateway.Dockerfile and updates the Docker entrypoint accordingly
• Adds a new development script dev/gateway that configures environment variables and runs the gateway on ports 5052 and 5057
• Reorganizes gateway-related environment variables under a dedicated section in dev/local.env
• Removes the required Prometheus registry check in pkg/api/server.go initialization
• Adds explicit chainRegistry.Start() call in pkg/gateway/builder.go
• Adds JSON contract configuration parsing to LoadConfigFromEnv function in pkg/gateway/helpers.go

📍Where to Start

Start with the LoadConfigFromEnv function in pkg/gateway/helpers.go to understand the configuration loading changes, then review the gateway builder initialization in pkg/gateway/builder.go.

Changes since #1003 opened

• Consolidated gateway script functionality by removing separate gateway script and incorporating its configuration into the run-gateway script [6a0daab]
• Updated environment variable configuration in the gateway script [6a0daab]

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Macroscope summarized 6a0daab.

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[neekolas]

There is already a dev/run-gateway that looks nearly identical to this

[mkysel]

oh. I will merge them