Remote variable array to support multiple variable files.

[bbrala]

This pull request enhances the handling of remote variable files by allowing multiple --remote-variables flags, enabling users to fetch and merge several variable files from different remote Git repositories. The changes update both the CLI interface and the internal logic to support arrays of remote variable sources and ensure the merged variables are correctly processed.

Support for multiple remote variable files:

• The --remote-variables CLI option now accepts multiple values (as an array), allowing users to specify more than one remote variable file. (src/index.ts, src/argv.ts, README.md) [1] [2] [3]
• The logic in VariablesFromFiles iterates over each provided remote variable source, fetches the variable files, and merges them using deepmerge to combine all variables into a single object. (src/variables-from-files.ts) [1] [2]

Testing and documentation:

• The test for remote variables was updated to use an array for remoteVariables, ensuring the new behavior is covered. (tests/test-cases/remote-variables-file/integration.test.ts)
• Documentation in README.md was updated to explain how to use multiple --remote-variables flags.

(the code was not generated with AI ;))

[bbrala]

Updated the PR to use the proper library, did need some extra checks around the return value of the yaml library since it is not very specific.