[OneDiscover] Add data table row `log.level` severity indication

[kertal]

📓 Summary

To allow visually indication and highlighting of configured rows of Discover's data table, the UnifiedFieldList should be extended to display configured color bars at the left side of a table row. As the first use case for this feature we show different colors depending on the log.level. Here is how it should look like

To be defined: log.level values (there can be multiple different for a severity level like err or error) to displayed colors table

✔️ Acceptance criteria

• Extend UnifiedDataTable to allow configuration color indicators by row
• Make use of color indication in Logs Contextual Presentation using the log.level field
  • The log.level to color matching should be implemented in a way that it's also available for the UnifiedHistogram. where we also intend to make use of this colors
• Given we already show color indication depending log.level in the table, colors should be changed to the new schema

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)