fix: Improve v2 packaging

[psteinbachs]

Packaging changes:

• Package name is now influxdb2 and conflicts with any previous influxdb package (including initial 2.0.0, 2.0.1, and 2.0.2 packages)
  • Requires explicit removal of previous package before installing new package
• Creates an /etc/default/influxdb2 file if non existent, which sets environment defaults
  • INFLUXD_CONFIG_PATH=/etc/influxdb/config.toml
  • INFLUXD_BOLT_PATH=/var/lib/influxd/influxd.bolt
  • INFLUXD_ENGINE_PATH=/var/lib/influxdb/engine
• Systemd service file now reads /etc/default/influxdb2
• Detects if v2 directory structure/files exist and outputs upgrade message if not
• Generates an upgrade script under /usr/share/influxdb/influxdb2-upgrade.sh
  • Runs 'influxd upgrade' with appropriate arguments
  • If exit code successful, outputs a message about further steps, v1 cleanup via helper script
  • If exit code unsuccessful, outputs a message about further steps, v2 cleanup via helper script

• Well-formatted commit messages
• Rebased/mergeable

[danxmoran]

Should we include this in CHANGELOG.md? For the ARM build I made a top-level callout, we could maybe broaden it to something like "packaging changes"

[danxmoran]