Gather stats for migrating domain registers (e.g. migration duration per account)

[fxamacker]

Related to onflow/cadence#3584

It would be useful to gather more stats related to migrating domain registers.

Currently, mainnet accounts have an average of about 4.4 domains (there are 9 domains available). Although duration of migration isn't unbounded, we should gather stats, investigate any surprises, and get a sense of batch size limits we should try during subsequent testing (before deploying to testnet).

Suggested Solution

Generate 5-number summary for the duration of migrating domains for each mainnet account. Optionally, include some other percentiles and some non-duration stats about migration if time allows.

If an account takes significantly longer than other accounts, investigate to see if we found an edge case.

Context

On Nov 26, a quick and dirty sanity check using old migration program didn't detect any edge cases that would take "minutes" for existing mainnet accounts. The worst case was roughly around 3s if we include overhead from old migration code (we expect slowest domain migration to be faster than that).