Corporate proxy not well supported

**Environment**:

- *Jib version:* last maven plugin
- *Build tool:* maven
- *OS:* redhat 8

**Description of the issue**:
The corporate proxy (http://user:password@host:port) is not well supported.

**Expected behavior**:
docker.io images can be pulled thanks the proxy.

**Notes**

* https://github.com/GoogleContainerTools/jib/blob/5e9a65f48a1631f32afbbe1bf5b574f38bb52d9c/jib-maven-plugin/src/main/java/com/google/cloud/tools/jib/maven/MavenSettingsProxyProvider.java#L90 references proxyUser/proxyPassword but it is not a JVM configuration whcih is supported so it does pretty much nothing.
* I didn't find how to force to use the proxy over http for https protocol in jib
* using maven proxies should be sufficient and is likely desired for maven integration (note that maven wagon - dependencies/plugins download - falls back on http proxy when the url is in https protocol properly which enables the previous use case to work transparently)