docs: Update gRPC spelling in READMEs (#13264)

That's it; AFAIK this is the correct spelling. Omitted the
`CHANGELOG.md` updates as I wasn't sure the process of backporting fixes
to release docs, or if those should be considered immutable.

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Jin Seop Kim <jinseop@google.com>

Author: 3 people

sdk-platform-java/gax-java/README.md

@@ -4,7 +4,7 @@ Google API Extensions for Java
 - [API Documentation](https://cloud.google.com/java/docs/reference/gax/latest/overview.html)
 
 Google API Extensions for Java (GAX Java) is a library which aids in the
-development of client libraries for server APIs, based on [GRPC](http://grpc.io)
+development of client libraries for server APIs, based on [gRPC](https://grpc.io)
 and Google API conventions.
 
 Application code will rarely need to use most of the classes within this

sdk-platform-java/hermetic_build/DEVELOPMENT.md

@@ -88,8 +88,8 @@ as per [POSIX env var definition](https://pubs.opengroup.org/onlinepubs/96999197
    ```shell
    unzip /path/to/zipfile -d "${HOME}/.library_generation/"
    ```
-#### Put the GRPC plugin in its well-known location
-1. Download GRPC plugin from [Maven Central](https://central.sonatype.com/artifact/io.grpc/protoc-gen-grpc-java/versions).
+#### Put the gRPC plugin in its well-known location
+1. Download gRPC plugin from [Maven Central](https://central.sonatype.com/artifact/io.grpc/protoc-gen-grpc-java/versions).
 2. Move the folder into its well-know location.
 
    ```shell