doc: fix link to be grpc link for HttpRequest

[cindy-peng]

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Fixes #799 🦕 Logging client library calls gRPC logging API instead of rest. This is to fix the documentation link for HttpRequest message to be correct gRPC link.

[generated-files-bot[bot]]

Warning: This pull request is touching the following templated files:

• README.md - README.md is managed by synthtool. However, a partials file can be used to update the README, e.g.: https://github.com/googleapis/nodejs-storage/blob/main/.readme-partials.yaml

[gkevinzheng]

I saw in some of the code comments links to the documentation of the JSON HttpRequest object. Could you update those code comments as well, for consistency?

[cindy-peng]

I saw in some of the code comments links to the documentation of the JSON HttpRequest object. Could you update those code comments as well, for consistency?

Good catch! Updated links in code comments as well.