[Doc] Use code injection tool to include code samples from compilable Java code in readme.

[mssfang]

To have a ReadmeSamples java file to maintain the codesnippet of readme file. So that make sure the readme codesnippet section is compilable.

E.x.,
comment to run: npx embedme sdk//azure-core/README.md
and file to take a look at
./src/samples/java/com/azure/core/http/netty/ReadmeSamples.java

[samvaity]

Resolved in #7118