[RELOPS-2104] linux snmp

[aerickson]

Replaces #1052 (new PR in this repo so windows integration tests will run).

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See https://mozilla-hub.atlassian.net/browse/RELOPS-2104.

Configure snmpd on 18.04 and 24.04 linux hosts.

DONE:

• puppet code
• spec tests & integration tests passing
• added way to disable (via hiera, set snmpd.enabled: false)
• testing on hardware hosts (18.04, 24.04)
  • including disabling snmpd via hiera / /root/vault.yml, setting snmpd.enabled: false

Also:

• run-puppet.sh: guards against non-root users