[Telemetry Operator] Support repeated keys in custom Fluent Bit plugins

[a-thaler]

Description

Fluent Bit output or filter plugin configurations might expect repeated keys. For instance, the header attribute of the HTTP output plugin can be set multiple times.

The telemetry-operator stores a configuration section internally in a map. When using repeated keys in a configuration section, oder the last occurrence of a key would be effective.

Criteria

• All occurrences of repeated configuration keys in custom plugin definitions need to be supported
• Attributes which are not repeatable should fail validation when multiple entries are provided