feat(memorystore): added valkey caching practical source-code samples

[dackers86]

Description

Fixes #<ISSUE-NUMBER>

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• [x] I have followed Sample Format Guide
• [ ] pom.xml parent set to latest shared-configuration
• [ ] Appropriate changes to README are included in PR
• [ ] These samples need a new API enabled in testing projects to pass (let us know which ones)
• [ ] These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• [x] Tests pass: mvn clean verify required
• [x] Lint passes: mvn -P lint checkstyle:check required
• [ ] Static Analysis: mvn -P lint clean compile pmd:cpd-check spotbugs:check advisory only
• [ ] This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• [ ] This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• [x] Please merge this PR for me once it is approved

[iennae]

@dackers86 you need to make sure that all files have the appropriate Apache 2 header please.

[telpirion]

Hello @dackers86 -- this PR needs a bit more work before we can accept it.

Before resubmitting, please be sure to review the Google Samples Style Guide and the SAMPLE_FORMAT guide before re-opening. I encourage you to look at other samples in this repository to see how samples are typically formatted and styled.

This PR needs to have the following global issues addressed:

• Provide region tags for the samples. memorystore is the prefix for this product.
• Provide samples integration tests.
• Provide a main method and a sample method in each code file. The main method passes arguments to the sample method.
• Remove static field declarations in the samples. See previous comment -- pass arguments from main to samples method.
• Remove unused, private constructors.