Support GraphQL user defined `operationName`

[nightroman]

For the moment, operationName is kind of supported but it is not really user defined and it has several issues as is. Details:

operationName is handled by this code

The issues:

Issue 1: This does not work if GraphQL starts with not query but comment (#), mutation, subscription, fragment.

Issue 2: Even with query it gets the name of the first query but the user wanted operation may be not the first operation. A user may work around by moving a selected query to the top but not mutation and subscription.

Suggestion: To make at least this possible for mutation and subscription, please change this line to this:

const matched = body?.match(/^\s*(?:query|mutation|subscription)\s+([^@\{\(\s]+)/i);

Issue 3: Even for queries (and mutations and subscriptions with the above suggestion) the included GraphQL file (< or <@) is not always suitable for changes.

Feature request:

The idiomatic suggestion is using the ad-hoc header X-GraphQL-Operation: {operationName}. It is consistent with the existing X-Request-Type: GraphQL approach with special treatment. Namely, if X-GraphQL-Operation: {operationName} is provided, HTTP Client uses it as operationName, no regex parsing is needed, it's the user choice.

Or, simpler but hacky: using some conventional suffix on file inclusion: e.g. < MyQueriesAndMutations.graphql:Query5 defines operationName as Query5. Caveat: This will not work for GraphQL inline body but users may have their wanted operation defined first (unlike with files, it's easy).

P.S. For what it's worth, I went with X-GraphQL-Operation: {operationName} in my project PSRest, REST Client features as PowerShell module. Interestingly, exactly this issue inspired me. Then I realized other useful features for PowerShell use cases, like using REST Client style environment variables for something else.