deployment: add starknet_url to hybrid environment overlays

[nimrod-starkware]

Add starknet_url to config.sequencerConfig in each production hybrid environment overlay:

• mainnet/common.yaml: https://feeder.alpha-mainnet.starknet.io/
• sepolia-alpha/common.yaml: https://feeder.alpha-sepolia.starknet.io/
• sepolia-integration/common.yaml: https://feeder.integration-sepolia.starknet.io/

Corresponding devops PR (removes the same key from the devops overlays): starkware-industries/sequencer-devops#701

[reviewable-StarkWare]

This change is 

[nimrod-starkware]

• deployment: define common env #14196
• deployment: add gcp pod monitoring to hybrid environment overlays #14192
• deployment: add liveness probe to hybrid environment overlays #14191
• deployment: add readiness probe to hybrid environment overlays #14190
• deployment: add startup probe to hybrid environment overlays #14188
• deployment: add monitoring endpoint port to hybrid environment overlays #14187
• deployment: add service ports to hybrid environment overlays #14185
• deployment: move network and consensus ports to hybrid environment overlays #14183
• deployment: add component ports and urls to hybrid environment overlays #14181
• deployment: add recorder_url to hybrid environment overlays #14180
• deployment: add starknet_url to hybrid environment overlays #14179 👈 (View in Graphite)
• main

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[cursor]

PR Summary

Medium Risk
Wrong feeder URL on production hybrid networks could misconfigure how the sequencer talks to Starknet; scope is limited to three YAML overlays.

Overview
Adds starknet_url under config.sequencerConfig in the three production hybrid overlay common.yaml files, each pointing at the matching Starknet feeder endpoint (alpha mainnet, alpha Sepolia, integration Sepolia).

This aligns hybrid deployment config with how other overlays already set feeder URLs; the paired devops change removes the same key from devops overlays so the value lives in one place per environment.

^{Reviewed by Cursor Bugbot for commit bfe2921. Bugbot is set up for automated code reviews on this repo. Configure here.}

[dorimedini-starkware]

@dorimedini-starkware reviewed 3 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on matanl-starkware).