Werk #10317: Readd SLES 12 SP3

Component	Linux distributions
Title	Readd SLES 12 SP3
Date	Nov 4, 2020
Level	Major Change
Class	New Feature
Compatibility	Incompatible - Manual interaction might be required
Checkmk versions & editions	2.0.0b1 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT

Readd Support for SLES 12 SP3, which was removed prematurly.

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