[Lens] Support for Gradient and Rainbow color palette in Lens

[rajvi-patel-22]

Describe the feature:

The TSVB visualization supports the below color palettes which also includes Gradient and Rainbow color palette.

The Lens supports the below color palettes which don't include Gradient and Rainbow color palette.

Describe a specific use case for the feature:

While migrating existing TSVB dashboards to Lens, it's quite hard to achieve the exact look and feel especially when breakdown functionality is used.

Here is the example of CockroachDB dashboard:

Most of the panels are created using a rainbow color palette. Now after migrating these panels to the lens, we would have to use the default color palette. Below, I have attached the screenshots for both scenarios:

Before Migrating to lens:

After Migrating to lens:

[elasticmachine]

Pinging @elastic/kibana-visualizations @elastic/kibana-visualizations-external (Team:Visualizations)

[stratoula]

The reason that we don't have the rainbow palette in Lens is that is not considered a best practices palette. We are not planning to add this in Lens but we are working on giving the option to give specific color by specific term and on custom palettes so someone could build it as it is. #101942
The same will apply for the gradient palettes.

[drewdaemon]

Closing this since we don't plan on adding these palettes.