Patch: Add Eltek OIDs RectifierTotalCurrent and RectifierUtilization

Hi All,

Just wanted to submit a patch I created which adds support for two additional fields from Eltek Power Systems supported already by the `../observium/includes/discovery/sensors/eltek-distributed-mib.inc.php` file. I talked to @FrogOfWar on your discord and he told me to post it here in an issue with a pastebin.

This patch adds support for the fields:

• Current - `RectifierTotalCurrent` (A)
• Load - `RectifierUtilization` (%)

File: `/opt/observium/includes/discovery/sensors/eltek-distributed-mib.inc.php`

Source: https://pastebin.com/ZZG0NkDB