Inform that repository indexing is in progress while using code search API

[henryju]

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Hi,

We are using the code search API to detect if a repository contains some specific files. The issue we are facing is that some users are using our service just after importing their repository, and so the file indexing is still in progress. When we call the search/code API, it returns an empty list, without any mention that indexing is in progress.
Doing the same in the UI, there is an indication:

Could we have the same in the REST API?