feat(deploy-config/getting-started): Clarify TIMESTAMP is int, not string

Closing: https://linear.app/optimism/issue/DEVRL-791/suggestion-l2outputoraclestartingtimestamp-needs-to-be-an-int-without

docs/op-stack/src/docs/build/getting-started.md

@@ -201,7 +201,7 @@ Once you’ve built both repositories, you’ll need head back to the Optimism M
     - Replace `"BATCHER"` with the address of the Batcher account you generated earlier.
     - Replace `"SEQUENCER"` with the address of the Sequencer account you generated earlier.
     - Replace `"BLOCKHASH"` with the blockhash you got from the `cast` command.
-    - Replace `"TIMESTAMP"` with the timestamp you got from the `cast` command. Note that although all the other fields are strings, this field is a number! Don’t include the quotation marks.
+    - Replace `TIMESTAMP` with the timestamp you got from the `cast` command. Note that although all the other fields are strings, this field is a number! Don’t include the quotation marks.
 
 ## Deploy the L1 contracts
 

packages/contracts-bedrock/deploy-config/getting-started.json

@@ -21,7 +21,7 @@
 
   "l2OutputOracleSubmissionInterval": 120,
   "l2OutputOracleStartingBlockNumber": 0,
-  "l2OutputOracleStartingTimestamp": "TIMESTAMP",
+  "l2OutputOracleStartingTimestamp": TIMESTAMP,
 
   "l2OutputOracleProposer": "PROPOSER",
   "l2OutputOracleChallenger": "ADMIN",