Document manual monorepo steps associated with a new upgrade (OPCM - Upgrade 13)

[maurelian]

When an upgrade occurs on Sepolia or Mainnet, it is likely that some of the ugprade tests may break, or else will just not accurately represent the actual upgrade process

For now this github issue, and comments on it, can be used for now to document any steps.

Known items:

1. The base chain may need to be update from Mainnet to Sepolia or vice versa.
2. FORK_BLOCK_NUMBER should be updated in the contract's justfile
3. Daily CI run upgrade tests may also need to be updated if the previous steps don't address any failures in them.
4. upgrade() methods in the contracts (usually only SystemConfig and OPCM) will need to be reset to empty.

[alcueca]

Two questions:

1. Would this go in a new section in the Optimism Docs ("Chain Upgrades")?

2. Is all the information that we need the four items in this issue?