3652 Catch APIError on multi-search requests due to bad query syntax

[albertisfu]

Most of the errors in #3652 relate to queries with incorrect syntax.
I described in #3171 the cases that seem different.

The problem was that previously, when using the Search API, it returned these kinds of errors as a RequestError, which we caught and logged as a warning.

The Multi-search API now raises an APIError instead with the message Failed to parse query ...

To stop raising these errors on bad query syntax and to display this screen to users instead:

Now it catch the APIError and only log a warning if the message error is Failed to parse query ....

• Additionally I believe there could be other types of APIError not related to query parsing because some of the errors logged in Sentry appear to have valid queries. However, the error message in Sentry just shows: ApiError /, so it's better to log an error with the full message so we can identify if there are additional APIErrors that we should handle or fix.

[mlissner]

Simple enough and a good improvement, thanks.