[TASK]: Implement accounts merging

Port the accounts merge frontend to Staking. Ensure L2 is supported.

[ ] PR https://github.com/Synthetixio/staking/pull/665
[x] Visit https://staking-git-feat-accounts-merge-synthetixio.vercel.app/merge-accounts
[x] Connect wallet if not already connected
[x] Switch to optimism
[x] Expect to be presented with 2 options (burn+nominate and merge).
[x] Click the first one (burn + nominate)
[ ] Expect to be presented with a burn screen if the wallet has a debt
[ ] Click the form button to burn the debt
[ ] Once the transaction concludes, click the "NEXT" button
[ ] Expect to be presented with a new form to nominate the address to send the vested snx
[ ] Enter the address and submit the form
[ ] Once the transaction concludes, click the "SWITCH TO DESTINATION ACCOUNT".
[ ] Expected to be presented with the merge form
[ ] On metamask, switch to the address that was nominated
[ ] In the form, enter the address you just switched form i.e. the address that contains the vested snx
[ ] Expect the form button to be enabled
[ ] Submit the form
[ ] Click "FINISH" once the transaction finished
[ ] Expect the dapp to redirect to the escrow form
[ ] Expect the source account vested snx to have been migrated to the current address

Synthetixio / issues