Handle rate limiting for ada-002 embedding model

[simonw]

Got this error:

openai.error.RateLimitError: Rate limit reached for default-text-embedding-ada-002 in organization org-2s2EXgTQ0xpZph33D2POEckd on tokens per min. Limit: 1000000 / min. Current: 598769 / min. Contact us through our help center at help.openai.com if you continue to have issues.

That was when I accidentally tried to embed a HUGE volume of content (I had meant to use sentence-transformers/all-MiniLM-L6-v2).