[Telemetry Manager] add priority class

[a-thaler]

Description
By default the module components should be scheduled with a higher priority then user workload to assure that system functionality is working preferred over custom workload. For that custom priority classes are needed. The user can explicit overrule the priority if he has reasons.
So introduce a priority class and assign it to all telemetry components.

Criteria

• As part of the managers kustomize files two priorityClass gets installed
• The manager and all subsequent components are setting these classes
• Current helm chart should already ship the new priorityClasses as well and decouble from the global setting
• An env test assures that the classes are set always
• Verify upgrade flow if fluent-bit takes new priority class
• Verify migration to modules work without hiccup

Related
kyma-project/community#768

[rakesh-garimella]

• The priority class has been added. They are passed in helm and also in the kustomize
• The migration test and upgrade test looks okay.
• Env tests have been added