Handling indexNotFoundError in populate cache

[pandu-k]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) Bug fix

• What is the current behavior? (You can also link to an open issue here) If an index mappings aren't retrievable, after get_indices on startup, Marqo can crash preventing proper startup

• What is the new behavior (if this is a feature change)? If an index mappings aren't retrievable, after get_indices on startup, Marqo simply ignores that index and moves on

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) No

• Have unit tests been run against this PR? (Has there also been any additional testing?) No. Test to make: concurrency test, testing for the failure scenario

• Please check if the PR fulfills these requirements

• [ ] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes/features)
• [ ] Docs have been added / updated (for bug fixes / features)

[vicilliar]

TODO: Finish tests

[farshidz]

Stale