fix(fetch): fix memory leak when passing keepAlive

[MichaelDeBoey]

See @marwan38's remix-run#24 & @donavon's remix-run#29

This is a direct copy of node-fetch/node-fetch#1474.

We're having memory leak issues as we're using a http agent with keepAlive options with the fetch used on the remix server.

CC/ @alanshaw @Gozala

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#77 needs to be merged first

[Gozala]

@MichaelDeBoey I'v attempted to resolve merge conflicts and reviewed changes. Have not merged it since PR is marked as a draft. If it's done feel free to merge.

[MichaelDeBoey]

@Gozala I don't have permissions to merge this branch, so you will need to do it
If you wish to add more maintainers to this package, I know @jacob-ebey and I would be happy to help out

[Gozala]

@Gozala I don't have permissions to merge this branch, so you will need to do it

I have invited to the contributors team earlier today, once you accept the invite you should be able to merge.

If you wish to add more maintainers to this package, I know @jacob-ebey and I would be happy to help out

Inviting @jacob-ebey to the team as well

[MichaelDeBoey]

I have invited to the contributors team earlier today, once you accept the invite you should be able to merge.

Didn't see that yet 🙈
Accepted now 😉

Inviting @jacob-ebey to the team as well

Thanks 🙏