Add APC Back-UPS ES 850G2

[SISheogorath]

Sanity check list

• [x] This PR is named to help easy searches (identify the vendor, device...)

• [x] Data dump file name follows this pattern (safely using ASCII characters): <manufacturer>__<model>__<driver-name>__<nut-version>__<report-number>.<extension> (more nuances are documented on site).

• [x] This file is placed into a sub-directory named same as the manufacturer.

• [x] Was this content prepared with nut-ddl-dump.sh script?

• [x] Information from upsc discovered fields is provided un-commented.

• [x] Additional data about supported RW variables and/or instant commands is provided (as comments)... (@SISheogorath: I hope the script does this automatically correct)

• [x] ...prefixed with standardized comment mark-up as documented on site, e.g.:

  #RW:<var.name>:<type>:<options>

  and

  #CMD:<command.name>

• [x] Mark-up for other structured comments is followed (for fields, vars, etc. as documented on site), where applicable.

• [x] For devices supported only with special settings in their ups.conf configuration section (e.g. vendorid and productid required along with a USB subdriver), example section content is welcome as a comment.

• [ ] For a newly discovered supported device, a sibling PR for the main NUT codebase (at least docs/driver.list.in, or possibly VID/PID and other auto-detection mapping tables in the driver sources) is welcome.

• [ ] This PR is linked to relevant issue(s) and/or PRs in the NUT project if applicable.

[SISheogorath]

I'm not entirely sure about what the do in the last 2 bullet points, so feel free to point me in the right direction :)

[jimklimov]

Sorry, this one fell through in my notifications.

The drivers.list.in bullet point referred to https://github.com/networkupstools/nut/blob/master/data/driver.list.in (thanks for the nudge, I updated the issue template now), to check if the submitted series/model is in that file too (the "HCL" part). This one is not, so a PR to add a line there would be needed too. Hopefully I'd get to sift through the large backlog of HCL/DDL reports to push them as one big PR in each repo...

[jimklimov]

Added the commit in NUT repo for a brewing PR with HCL/DDL updates.