feat(anvil): allow pass headers to fork-url

[vbrvk]

Closes #6173

[vbrvk]

After added headers param clippy does not satisfied with too many arguments. @Evalir what do you think the best option to fix it?

[mattsse]

please rm all additional ;

makes it harder to review

[vbrvk]

Fixed, actually I was thinking about not adding them, but contributing guide recommends to enable formatOnSave option, so I did :)

[Evalir]

yep @vbrvk we use nightly clippy/formatting, so the appropiate command should be cargo +nightly fmt—we can probably make this a bit clearer in the contribution guide

[mattsse]

lgtm!

ty