Add the ability to pass through the keepalive configuration option

[brendon]

I have a few concerns:

• We're hard coding the current defaults for fetch for many options. Why not just omit passing them if they're not passed in?
• It might be more future proof to allow any options to be passed in, and just override those specific options like contentType and headers as needed.

The solution to those is a much larger change, so for now just allowing keepalive through solves my immediate use-case.

Closes #85

[brendon]

CI needs some fixing :)

[marcelolx]

@brendon do you mind rebasing from main now that #88 has been merged?

I am fine with us going only with keepalive for now and then later support customizing all other options

[brendon]

Hi @marcelolx, all done :)

[brendon]

Hi @marcelolx, would you mind cutting a new release with this fix in it? :)

[marcelolx]

Done @brendon