Add support for external user identity fetching

[Starefossen]

This pull request includes several changes to the README.md, __tests__/main.test.ts, action.yml, package.json, and src/index.ts files to add new features, update dependencies, and improve error handling. The most important changes include adding support for external user identities, updating dependencies, and improving error handling.

New Features:

• Added support for external user identities in the README.md, action.yml, and src/index.ts files. This includes adding a new input parameter external-identities, fetching external identity information, and updating the inactive seats data with this information. [1] [2] [3] [4] [5] [6] [7] [8]

Documentation Updates:

• Updated the README.md file to include new sections and examples for the external-identities input parameter and other minor formatting adjustments. [1] [2] [3] [4] [5] [6] [7] [8]

Dependency Updates:

• Updated several dependencies in the package.json file to their latest versions, including @actions/artifact, @actions/core, @octokit/request-error, @octokit/types, csv-parse, @types/jest, @types/node, @typescript-eslint/eslint-plugin, @typescript-eslint/parser, @vercel/ncc, jest, ts-jest, ts-node-dev, and typescript.

Testing Improvements:

• Updated the __tests__/main.test.ts file to include new test input parameters and additional logging for better test coverage and debugging. [1] [2]

Error Handling Enhancements:

• Improved error handling in the src/index.ts file by dynamically importing the RequestError class and refining error messages for better clarity. [1] [2] [3] [4]