Expose search endpoint via our web api

[humphd]

What would you like to be added:

We need to expose search via our service API. In the simplest case, this could mean doing something like ?q=searchTerm. This should return the posts that we have which match that search.

Here are some things to research:

• GitHub does it like this: https://developer.github.com/v3/search/
• Shopify does it like this: https://help.shopify.com/en/api/getting-started/search-syntax#search-query-syntax

At first, we don't need a lot of complex criteria for this, and it can evolve over time.

Why would you like this to be added:

We're adding full-text indexing and search in #537. This will expose it to our frontend as a service.

[humphd]

I'm unclear how to expose this as part of graphql. That might need another issue.