Allow customization for extensions type

[dodomorandi]

Description

This introduces a new configuration for the graphql-request plugin for
typescript. It allows to use unknown (or a custom type) instead of
any for the extensions parameter without breaking changes.

Related dotansimha/graphql-code-generator-community#156

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

No jest tests has been added for this. The change is trivial, but if you want me to add a test, just say it.

Checklist:

• I have followed the CONTRIBUTING doc and the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes -- Only if I only run tests related to the plugin, otherwise I have lots tests that don't pass, like in master

[changeset-bot]

🦋 Changeset detected

Latest commit: 69a99bb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@graphql-codegen/typescript-graphql-request	Minor

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[n1ru4l]

@dodomorandi Can you please create a changeset that describes this change? See #6969 (comment)

[dodomorandi]

Thanks @n1ru4l for the feedback! Let me know if you want me to squash the commits (now or later).

[n1ru4l]

@dodomorandi Sorry one more thing, could you add a very simple test for verifying that this option does not break in the future? 😇 No worries about squashing, I will do that during the merge!

[dodomorandi]

No problem! I was doubtful just because it will be more complex the test than the actual feature 😁. I am going to add the test and update the checklist.

[n1ru4l]

@dodomorandi The downside of having lots of options is that you can sometimes break them without noticing 😆 Which unfortunately happened a lot lately.

[n1ru4l]

@dodomorandi Awesome thank you!