Docs: add basic grpc example

[ciarams87]

Proposed changes

Problem: We need an easy way to configure and test GRPCRoute examples

Solution: Add a basic example with a sample hello world application and configurations for the 3 primary gRPC routing methods

Testing: Ran through the example locally

• See GRPCRoute Support #1835 (comment) for context

Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

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