Update Flashblocks availability for Optimism mainnet (#898)

Author: oskarciupider-alchemy

fern/api-reference/op-mainnet/op-mainnet-flashblocks-api-quickstart.mdx

@@ -18,7 +18,7 @@ Flashblocks is currently supported on both Optimism Sepolia testnet and mainnet
 | Network       | Flashblocks Availability |
 |---------------|---------------------------|
 | Optimism Sepolia  | ✅                        |
-| Optimism Mainnet  | TBA                        |
+| Optimism Mainnet  | ✅                        |
 
 ## Flashblocks-enabled API Endpoints