Add proxy support

[alxgarder]

I can see that a request for proxy support was raised in 2022 and closed without a commit. Does this mean you do not intend to add proxy support at all?

This works great in the ACI provider, which honors the "HTTP_PROXY" environment variable, so Im a little baffled why its not part of the fmc provider.

Link to old issue #17

[danischm]

netascode/go-fmc@5774679

[danischm]

f563a53

[rchrabas]

Relevant changes were made to the main branch. This will be available with 2.0.0-beta4 release.