Add an `Object.groupBy` TypeScript goody

[miorel]

An Object.groupBy method is being added to JavaScript, but for now this is not available on LeetCode, since it requires Node 21, whereas LeetCode uses Node 20.

We'd like to get access to this function sooner, so let's create our own version!

This issue involves adding another directory within workspaces/adventure-pack/goodies/typescript, named Object.groupBy, with an index.ts for the implementation and an index.test.ts for a test. You can use the Map.groupBy added by #358 for inspiration, this should be very similar.

Note: after adding or updating a goody you will need to run yarn package-goodies:test -u to refresh the snapshot tests.

Please comment with any questions.

[elimanzo]

@miorel Quick question would this issue be the same as #108

[miorel]

Not exactly. This one is about replicating the built-in function Object.groupBy, #108 would be about adding a method to iterators.