[DOCS] Deprecate central management

[dedemorton]

Closes #14045. Adds deprecation statement to the topics about central management. Also removes docs that points users to central management because I don't think we should be directing users to use a feature that's not deprecated. We will replace the references when docs for our CM replacement are in place.

TODO:

• Merge Add shared file for discontinued features docs#1354 before merging this PR.
• Add the shared statement to the Kibana docs: https://www.elastic.co/guide/en/kibana/7.4/managing-beats.html

[mattapperson]

@dedemorton I am not sure we want to state it is deprecated as of 7.5. Technically it has been deprecated, we are just being more upfront about it now

[dedemorton]

@mattapperson I wonder if we should say "discontinued" instead of "deprecated." I'm not sure how we've handled this in the past. It would be nice to have some standard text that we can provide when we decide to discontinue a beta feature. @debadair Does the Elasticsearch team have a convention for flagging beta features that are discontinued?

[debadair]

I think discontinued is the right term to use here. Elasticsearch follows a specific process for marking existing (GA) features as deprecated and ultimately removing them. I didn't find any examples in ES, but we used discontinued for an ES Hadoop beta feature that was removed:

YARN Integration Discontinued
Due to the limitations in YARN for support of long running processes, we have decided to cease development and discontinue the YARN integration in ES-Hadoop. We thank the community for participating in the beta. If you have any questions or concerns about this, please feel free to discuss them on our forums.

We don't have a built-in widget for this like deprecated. Maybe format it as a sidebar?

.Beats central management discontinued
**** 
We have ceased development on Beats central management and 
are working on a comprehensive solution to replace it. 
Thank you for participating in the beta and providing feedback. 
If you have any questions or concerns, please reach out to us on the
https://discuss.elastic.co/c/beats[Discuss forum].
****

I'm generally not a fan of "please" and "thank you" in the docs, but this is a case where it probably makes sense.

Whatever you decide to do, it would be good to "templify" it and put it in the docs/shared folder.

[dedemorton]

@mattapperson I like Deb's suggestion. If it looks good to you, I will change the text accordingly.

[ph]

look OK on my side @dedemorton and @debadair

[mattapperson]

@dedemorton yup, looks good to me

[dedemorton]

I added a statement to the docs repo that we can include in any books that mention Central management: elastic/docs#1354

[dedemorton]

@elasticmachine run elasticsearch-ci/docs

[dedemorton]

jenkins test this please

[dedemorton]

travis-ci is incorrectly reporting an error. Since this PR passes the doc check under beats-ci and elasticsearch-ci/docs, I'm merging.