Allow filtering requests to engine plugin endpoints

[paritosh-08]

Component

Graphql engine plugins

Is your proposal related to a problem?

Currently there is no way to configure the engine plugin to selectively trigger the
API endpoint.

Imagine a use case where the graphql endpoint receives a lot of graphql queries
and only a few mutations and I want to do some business logic for mutations only.
With the current configuration, you will have to do this filtering in the plugin API
handler itself, which means most of the requests to the plugin endpoint will be
discarded.

Describe the solution you'd like

If we could somehow add some filtering on the engine side itself, we can save on
some network calls and also have better latency for the graphql API.

Describe alternatives you've considered

The alternative here is to handle this filtering on the plugin endpoint handler, which
is not a good solution as we are wasting a lot of resource in handling the requests
that should not have triggered the endpoint in the first place.