Update snmp_exporter from 0.26.0 to 0.28.0

[prometheus-rpm-bot]

https://github.com/prometheus/snmp_exporter/releases/tag/v0.28.0
Release notes:

BREAKING CHANGES:

In this version of the exporter the sysUpTime metric has been removed from the if_mib module and 
is now part of the new system module, along with other useful system related metrics.
Please update your scrape definitions to include the system module if you need sysUpTime.

* [ENHANCEMENT] allow module-qualified labels in generator #1333
* [ENHANCEMENT] add healthcheck endpoint #1358
* [ENHANCEMENT] Override Metric Name in Generator #1341
* [BUGFIX] cleanup docker container after running #1330

snmp.yml changes:
* moved system related oids to the new system module #1334
* add UBNT AirOS module, DLink and Eltex MES #1344
* add JunOS module #1348
* enhancements on the hrStorage module, cleanup unused lookups for mikrotik module #1349
* update JunOS module and add Juniper Optics (DOM) module #1351
* added page counters to the printer module #1353