[BEAM-12368] Updated doc nav to match wireframe

[pcoet]

This PR changes the left nav to more closely match the wireframe. There are still some rough edges in the user experience, but it's better than the current nav, where the "Beam programming guide" node is not collapsible.

@aaltay
@tysonjh

NOTE: The diff is hard to read, with all of the HTML copy-paste. It's easier to just look at the staged site and compare it to the prod site, to see what's changed. All of the individual pages should still be findable in the nav.

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ValidatesRunner compliance status (on master branch)

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---					---
Java
Python	---					---
XLang						---

Examples testing status on various runners

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---	---	---	---	---	---	---
Java	---		---	---	---	---	---
Python	---	---	---	---	---	---	---
XLang	---	---	---	---	---	---	---

Post-Commit SDK/Transform Integration Tests Status (on master branch)

Go	Java	Python

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website	Whitespace	Typescript
Non-portable
Portable	---			---	---	---

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI.

[aaltay]

Looks great. Should we alphabetically sort the left nav? Or perhaps go in some logical order like starting from concepts etc. before going into details?

[pcoet]

Yup, I agree that the first ordering wasn't great. Alphabetical order is more useful when users already know what they're looking for -- I think we're better off with a logical order, which to me means a learning path. I reordered with what seems natural to me -- start with concepts and programming guide, and end with reference material and glossary. What do you think?

[aaltay]

Yup, I agree that the first ordering wasn't great. Alphabetical order is more useful when users already know what they're looking for -- I think we're better off with a logical order, which to me means a learning path. I reordered with what seems natural to me -- start with concepts and programming guide, and end with reference material and glossary. What do you think?

Great, thank you.

I was wondering if "Pipeline development lifecycle" would be better before programming guide, but I do not have a strong opinion. Let's go wit this version.