docs: add migration guide for upgrading from v1 to v2#76

zeke merged 17 commits intonextreplicate/replicate-python-beta:nextfrom

dp-684-write-a-migration-guide-for-users-upgrading-from-v1-to-v2replicate/replicate-python-beta:dp-684-write-a-migration-guide-for-users-upgrading-from-v1-to-v2Copy head branch name to clipboard