Change application port and command in Blockscout launch instruction

[vbaranov]

Description

Change explorer (Blockscout) running instructions:

• change explorer port 4000 -> 80
• clone production-optimism branch
• launching command is changed: specific to OP-stack docker image is used and the name of config.yml is changed.

Additional context

This should be merged after https://github.com/blockscout/blockscout/pull/8956 merged.

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