chore!: upgrade @oclif/core to v4 and update plugin development docs

[AshAnand34]

Fixes #647

This pull request includes multiple updates to dependencies, code refactoring, and test improvements. The most significant changes involve upgrading the @oclif/core dependency to version 4, replacing deprecated methods, and improving test assertions for better compatibility and readability.

Dependency Updates:

• Upgraded @oclif/core from version ^1.16.0 to ^4.3.3 in package.json to use the latest features and improvements.

Code Refactoring:

• Replaced oclifFlags with Flags from the updated @oclif/core package in src/commands/debugger/logs/list.js and updated flag definitions to use Flags.string instead of oclifFlags.string or oclifFlags.enum.
• Changed flags.enum to flags.string for several flag definitions in src/commands/phone-numbers/update.js to align with the updated @oclif/core API.
• Removed the unused compact import from @oclif/core/lib/config/util and replaced its usage with a direct .filter(Boolean) call in src/services/twilio-help/twilio-command-help.js.

Test Improvements:

• Updated test assertions in test/hooks/init/buy-phone-number.test.js and test/hooks/init/twilio-api.test.js to use optional chaining (?.) and fallback values for better compatibility with undefined properties.
• Replaced the deprecated trimRight method with trimEnd in test files test/services/twilio-help/twilio-help-doc.test.js and test/services/twilio-help/twilio-help.test.js for consistency and modern syntax.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.