Run single relayer in cluster script by default

[Stefan-Ethernal]

Description

Cluster script now runs single relayer by default, in order to be able to execute bridge transactions out of the box.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Manual tests

Please complete this section if you ran manual tests for this functionality, otherwise delete it

Documentation update

Please link the documentation update PR in this section if it's present, otherwise delete it

Additional comments

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