New ThreadPool are constantly being created on every http request

[tdraier]

Describe the bug When using OsgiGraphQLHttpServlet, a new thread pool (of 1 thread) is created on every request, and never shut down. The thread pool is created when creating a GraphQLConfiguration - if no asyncExecutor was provided (which is not possible when using OsgiGraphQLHttpServlet), a new ThreadPoolExecutor is created, without keeping any reference on it, and so never shutting it down. Creating a thread pool transparently without shutting it down is already an issue, but moreover OsgiGraphQLHttpServlet.getConfiguration() is creating a new configuration on every call, which is actually happening in AbstractGraphQLHttpServlet.doRequest() .

To Reproduce Steps to reproduce the behavior:

1. Create an OsgiGraphQLHttpServlet
2. Make http requests
3. Check the total number of threads

Expected behavior

• Don't create a pool automatically, or ensure it's properly closed when it's not used anymore
• Don't build new configuration every time we call getConfiguration
• Make it possible to pass a custom pool when using OsgiGraphQLHttpServlet. Ideally, it would be nice to be able to pass a full configuration (maybe through a "GraphQLConfigurationProvider")

I will try to provide a PR soon