[kibana] [vega] Fix broken help link on text editor

[a03nikki]

Kibana version: 7.10.1

Elasticsearch version: 7.10.1

Server OS version: Unknown as Cloud on GCP

Browser version: Firefox 84.0.1

Browser OS version: MacOS 10.15.7

Original install method (e.g. download page, yum, from source, etc.): Elasticsearch Service

Describe the bug: The help link to the documentation from the Vega editor's (?) icon returns 404.

Steps to reproduce:

1. Menu: Kibana > Visualize
2. Button: Create visualization
3. Type: Vega
4. Use the small help icon (?) and select the Kibana Vega help link
5. The link opens https://www.elastic.co/guide/en/kibana/master/vega-graph.html which returns a 404 page not found error

Expected behavior: Link to https://www.elastic.co/guide/en/kibana/7.10/vega-reference.html where the version number matches the version of Kibana similar to the help icon () in the top menu bar.

Screenshots (if relevant):

Link opens to a page that states

404
Well, that about wraps it up for this page

`I refuse to prove that I exist,’ says Page, `for proof denies faith, and without faith I am nothing.’

`But,’ says Man, `The Babel fish is a dead giveaway, isn’t it? It could not have evolved by chance. It proves you exist, and so therefore, by your own arguments, you don’t. QED.’

`Oh dear,’ says Page, `I hadn’t thought of that,’ and promptly disappears in a puff of logic.

Errors in browser console (if relevant): N/A

Provide logs and/or server output (if relevant): N/A

Any additional context: I think this has been broken for at least a few releases now.

[elasticmachine]

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

[KOTungseth]

Thanks for opening this @a03nikki! We'll wrap in this fix with the other broken links closer to the 7.11 release date.

[gtback]

It looks like, starting in 7.11, the page is just https://www.elastic.co/guide/en/kibana/7.11/vega.html