[skip-ci] Temporarily remove visualization development docs.

[lukeelmers]

Summary

Based on discussions with @flash1293, @elastic/kibana-app-arch, and others, we've decided to temporarily remove the visualization development docs starting in 7.5 to prevent confusion amongst both Elastic & community developers.

The APIs for creating custom visualizations are in a state of heavy churn as they are being migrated to the new platform, and large refactorings have been happening across minor releases in the 7.x series.

We expect to be able to re-add proper documentation later in 7.x when the visualizations plugin has been migrated and the APIs are in a more stable state, but in the interim the old docs are more likely to cause confusion than to be useful.

For those who would like to follow along with progress on the visualizations plugin in the meantime, I'd recommend the following resources:

• Meta issue which is tracking the move of the plugin to the new platform
• The breaking changes section of our documentation, where we try to capture any changes to the APIs as they occur across minors.

[elasticmachine]

Pinging @elastic/kibana-docs (Team:Docs)

[flash1293]

Do we want to leave a paragraph about being aware of this gap and it’s recommended to wait for another version till upgrading plugins? Unsure whether that’s even the best suggestion we can make but it feels to me like we should at least explain the absence in a few words.

[lizozom]

@elasticmachine merge upstream

[lizozom]

LGTM, but I agree with @flash1293

[flash1293]

Placeholder message LGTM, thanks for taking care of this

[weand]

is there an ETA when an official documentation will be added back? a lot of transition work seems to be done already.

[axelv]

Any pointers to some preliminary documentation or example code to get started developing a visualisation plugin on the NP?

[lukeelmers]

@axelv The best place for examples right now is probably the source code itself - you might check out a smaller visualization plugin like the one for the metric visualization.

I believe work is already underway on either documentation or a how-to blog post, but @elastic/kibana-app would be able to confirm.