Add explicit support for a proxy and bump scanner version

What's Changed

• Add explicit support for using a proxy by @csturiale in #154
• Bump scanner version to 4.7.0.2747 by @dzienisz in #151
• Fix sonar.links.issue incorrect naming by @ugrave in #160
• Fix documentation link about alpine by @sebaplaza in #134
• Improve documentation for using custom scanner path by @romanbalayan in #157

Milestone: https://github.com/bellingard/sonar-scanner-npm/milestone/19?closed=1
Full Changelog: 2.8.1...2.9.0