Update Besu/Teku tutorials to use checkpoint sync

[alexandratran]

Update the Besu/Teku Mainnet and testnet tutorials to use checkpoint sync when starting Teku. Make the same updates as those made to the Teku Mainnet/testnet pages in this Teku docs PR.

[MadelineMurray]

Checkpoint sync still in experimental mode at this stage on Besu so leaving this one for now.

[alexandratran]

@MadelineMurray This issue is just to update the example for Teku (which recommends checkpoint sync), and not the Besu example.

Specifically, we want to update this Mainnet tutorial section in the Besu docs to match this Mainnet section in the Teku docs, and update this testnet tutorial section in the Besu docs to match this testnet section in the Teku docs.

[MadelineMurray]

@alexandratran - gotcha. Thanks for the context. Will update.