Current syntax throws inaccurate error in op-proposer start script

[cspannos]

Description
Absence of the '=' symbol in the script to start op-proposer throws a misleading error.

Tests
The existing script:

./bin/op-proposer \
    --poll-interval 12s \
    --rpc.port 8560 \
    --rollup-rpc http://localhost:8547 \
    --l2oo-address $L2OO_ADDR \
    --private-key $PROPOSER_KEY \
    --l1-eth-rpc $L1_RPC

produces this error:
t=2023-06-28T15:16:56+0000 lvl=crit msg="Application failed" message="flag l1-eth-rpc is required"

Updating the script with =:

./bin/op-proposer \
    --poll-interval=12s \
    --rpc.port=8560 \
    --rollup-rpc=http://localhost:8547 \
    --l2oo-address=$L2OO_ADDR \
    --private-key=$PROPOSER_KEY \
    --l1-eth-rpc=$L1_RPC

produces what I assume to be an accurate error:

INFO [06-28|15:22:40.444] Initializing L2 Output Submitter 
ERROR[06-28|15:22:40.444] Unable to create the L2 Output Submitter error="invalid address: " 
CRIT [06-28|15:22:40.444] Application failed                       message="invalid address: " 

• Fixes #[Link to Issue]
  op-proposer failing #6174

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[tynes]

Thank you for this fix

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This PR has been added to the merge queue, and will be merged soon.

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