fix: add authority header

[vanhtuan0409]

Description

Some GRPC servers will return PROTOCOL_ERROR when missing HTTP2 :authority header. Eg: https://www.npmjs.com/package/@grpc/grpc-js

Thus preventing custom GRPC plugins

Related Issue

https://github.com/TykTechnologies/tyk/issues/3082

Motivation and Context

Allow custom GRPC plugins to use the latest nodejs GRPC sdk

How This Has Been Tested

Added unit test

Screenshots (if appropriate)

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Refactoring or add test (improvements in base code or adds test coverage to functionality)

Checklist

• [x] Make sure you are requesting to pull a topic/feature/bugfix branch (right side). If pulling from your own fork, don't request your master!
• [x] Make sure you are making a pull request against the master branch (left side). Also, you should start your branch off our latest master.
• [x] My change requires a change to the documentation.
  • [ ] If you've changed APIs, describe what needs to be updated in the documentation.
  • [ ] If new config option added, ensure that it can be set via ENV variable
• [ ] I have updated the documentation accordingly.
• [x] Modules and vendor dependencies have been updated; run go mod tidy && go mod vendor
• [ ] When updating library version must provide reason/explanation for this update.
• [x] I have added tests to cover my changes.
• [ ] All new and existing tests passed.
• [x] Check your code additions will not fail linting checks:
  • [x] go fmt -s
  • [x] go vet