Doc: Implement install widgets with platform tabs

[karenzone]

Release notes

[rn:skip]

What does this PR do?

Adds tab widget infrastructure
Breaks up walls of text by adding tabbed widgets to show installation instructions per platform

PREVIEW: https://logstash_12850.docs-preview.app.elstc.co/guide/en/logstash/master/installing-logstash.html
Check out the DEB x86_64 tab for a sample of what both DEB platform install instructions might look like under one tab.

IMPORTANT: This work is still in the design/experimental phase, and install content is not accurate.

ToDO:

• Finalize content
• Remove components used for local testing:
  • widgets code file (as indicated here)
  • hard-coded "released" setting that makes it possible to test content

[karenzone]

Status: 2021-0423

Added test scenario under deb-x86_64 tab. (Test scenario must be backed out before this PR can be merged.)

Next steps (notes to self @karenzone ):

• Get input on combining x86_64 and AARCH64 for each platform under one tab (LINUX, DEB, RPM, etc.) to shorten tab names and prevent ugly wrap scenario.

• Remember that selected platform persists. Grouping x86_64 and AARCH64 under one platform tab heading (Linux, DEB, RPM, etc.) might not be ideal for long text blocks (if we have a need for those). But the long, wrapping tab row isn't ideal either.

[karenzone]

@elasticmachine run elasticsearch-ci/docs

[karenzone]

@elasticmachine run elasticsearch-ci/docs

[karenzone]

jenkins test this please

[gtback]

@elasticmachine run elasticsearch-ci/docs

[gtback]

@elasticmachine run elasticsearch-ci/docs

[gtback]

@elasticmachine run elasticsearch-ci/docs

[karenzone]

@elasticmachine run elasticsearch-ci/docs

[karenzone]

ToDo: Figure out which tab should be the default selection, and set it.

[gtback]

I don't think we need to include this anymore since as of elastic/docs#2180, this is included in the doc build itself and doesn't need to be in each repo that uses the tab widgets.

[karenzone]

NOTED for future action. Thanks for the info. While I'm still developing content, it's handy to be able to fire off local builds for quickie testing.

I'll remove the file before I finalize this PR.

[gtback]

Sounds great, let me know if I can help at all.