feat: adding support for cookies to oas-to-har

[erunion]

🧰 What's being changed?

This adds general support for cookie parameters into the explorer and our oas-to-har library.

Adding this because it's a deficiency of our OpenAPI support, and also the new api should support it and that uses oas-to-har for the bulk of its processing. If you click on "Node (simple)" in the demo site you'll see that it currently doesn't support cookies (see readmeio/api#38).

🧪 Testing

I've added a grip of tests for cookies into the oas-to-har suite, all of which are identical to our tests for query string params. To see this in action, load up the demo site and check out the new cookies example:

🗳 Checklist

💡 If answering yes to any of the following, include additional info, before/after links, screenshots, etc. where appropriate!

• 🆕 I'm adding something new!
• 🐛 I'm fixing a bug!
• 📸 I've made some changes to the UI!

[rafegoldberg]

Read through this last night. Looks good to me.