Build failure with `exactOptionalPropertyTypes` enabled

[jhasuraj01]

Is your feature request related to a problem? Please describe.

Building the project using this library fails when exactOptionalPropertyTypes is enabled in project's tsconfig.json unless skipLibCheck is also set to true. skipLibCheck bypasses type checking for third-party libraries, compromising type safety.

Describe the solution you'd like

• Add the exactOptionalPropertyTypes property to oclif/core's tsconfig.json.
• Make any necessary code changes to ensure successful build with this option enabled.

Example rc/config/plugin.ts#L85:

From	To
{ parent: Plugin | undefined; }	{ parent?: Plugin; }

Additional context

• This change will improve type safety, leading to fewer potential runtime errors.
• It demonstrates adherence to best practices for TypeScript projects.

I would be happy to come up with a PR or collaborate on a potential solution.