Adding support for ppc64le.

### Describe the feature or problem you’d like to solve

Hi team, in reference to #3615, requesting to add ppc64le support.

### Proposed solution

I was able to build gh-cli from source following the instructions mentioned in https://github.com/cli/cli/blob/trunk/docs/source.md. I was also able to test the binary succesfully. Attaching below the build and test logs for the same.
[gh-cli-logs.txt](https://github.com/cli/cli/files/14019675/gh-cli-logs.txt)

I will raise a PR shortly. Thank you.

### Additional context

We are working on supporting OpenSearch distribution for ppc64le architecture, which has a dependency on gh-cli. https://github.com/opensearch-project/opensearch-build/issues/3122#issuecomment-1888049652

Start with docs/source.md and review the attached gh-cli build and test logs to understand the reported ppc64le process. Confirm the existing build instructions and tests work for ppc64le, then define done as a successfully built and tested gh binary for that architecture.

Escrito por el modelo de indexación a partir del texto del issue.