[FLINK-38945][docs][FLIP-561] Restructure Flink documentation

[MartijnVisser]

What is the purpose of the change

• Implement the proposed changes from https://cwiki.apache.org/confluence/display/FLINK/FLIP-561%3A+Restructure+Flink+documentation

Brief change log

This PR contains multiple commits, that should ultimately be squashed before merging. What's basically done is:

1. Move the content to the right new location, change refs and add aliases for redirecting users to the new pages
2. Add stub pages that redirect to the new location, given that externalized connectors docs are sometimes pointing to pages that no longer exist there, but have been moved. But we can't update the external connector docs because the new locations don't exist yet. This needs to be fixed afterwards
3. Added new content for Getting Started and Learn Flink sections where needed
4. Rewrote "First Steps" completely
5. Added a Table API archetype

I also included a couple of nice to haves/extra:

6. No longer show Google Analytics warnings when building the docs
7. Fixed a JS sync bug in the docs when you were switching between different languages (Java/Scala/Python) and the browser not updating the right tab anymore
8. Added a copy button for code blocks

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.
Verification has happened by checking out the PR and building it with Hugo locally

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no ****/ don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[flinkbot]

CI report:

• c4e22ad Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[rionmonster]

@MartijnVisser

Thanks for the PR!

I've been following the restructuring efforts on the mailing list, so I'm glad to see it progressing., I noticed a handful of RAT-related failures when attempting to build things locally which triggered a validation failure with was also reflected in CI:

[ERROR] Failed to execute goal org.apache.rat:apache-rat-plugin:0.13:check (default) on project flink-parent: Too many files with unapproved license: 41 See RAT report in: /Users/rion/dev/flink/target/rat.txt -> [Help 1]

I'm sure it's a trivial fix. I'll try to carve out some time to build and explore the updated documentation with these changes and approve if all looks good!

[MartijnVisser]

@flinkbot run azure

[rionmonster]

I'm not sure if it's a local development issue specifically, but it appears that none of the images are rendering properly. I suspect it's potentially a directory-shift that occurred during the updates?

[MartijnVisser]

I'm not sure if it's a local development issue specifically, but it appears that none of the images are rendering properly. I suspect it's potentially a directory-shift that occurred during the updates?

Yeah this is a local development problem specifically, it happened for all images. The image shortcode didn't properly work with baseURL for local builds. That should be fixed now, thanks for flagging!

[rionmonster]

Yeah this is a local development problem specifically, it happened for all images. The image shortcode didn't properly work with baseURL for local builds. That should be fixed now, thanks for flagging!

Thanks for the clarification @MartijnVisser, I figured as much. Just confirmed that the latest commits addressed the previous RAT-related licensing issues (and Azure seems to agree). Approving — thanks again!