feature: Extract interface from DefaultDgsGraphQLContextBuilder

[nallwhy]

Describe the Feature Request

To support multiple custom contexts, changing DefaultDgsGraphQLContextBuilder with another class should be available.

Describe Preferred Solution

For that, DgsGraphQLContextBuilder interface should be made and many codes that depend on DefaultDgsGraphQLContextBuilder should depend on DgsGraphQLContextBuilder interface.

It meansDefaultDgsGraphQLContextBuilder became a just one of implementation of DgsGraphQLContextBuilder.

Describe Alternatives

I have no idea.

[nallwhy]

If this idea is OK, I can contribute to it.

[srinivasankavitha]

I'm not sure I understand the use case. You can already build a custom context using the context builder. I don't quite see the need for a different implementation of the DefaultDgsGraphQLContextBuilder.

[nallwhy]

Can I build multiple custom context with DefaultDgsGraphQLContextBuilder? As I know, graphql-java supports multiple custom context.

ex) AuthContext, DeviceContext, ...