[FLINK-20832][docs] Deliver bootstrap css and js ourselves

[wuchong]

What is the purpose of the change

Delivering the required files ourselves, instead of using a CDN to fix the unstable https://maxcdn.bootstrapcdn.com in China.

Brief change log

• Copy the resource files into docs/page/...
• Update the base.html.

Verifying this change

I shutdowned the network on my machine, and locally build the docs, and everything works well.

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, Yarn/Mesos, 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)

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Automated Checks

Last check on commit 4a04180 (Fri May 28 07:03:23 UTC 2021)

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[rmetzger]

Thanks for opening the PR. Have you checked the licenses of the font files?

[wuchong]

@rmetzger , no, I just download them from the bootstrap CDN url.
How do we deal with the existing docs/page/font-awesome/fonts/FontAwesome.otf?

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CI report:

• dd86f51 UNKNOWN
• 4a04180 Azure: SUCCESS

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[rmetzger]

It's mentioned in the /NOTICE file.

[rmetzger]

I believe we should mention this dependency in the NOTICE file and add a copy of the license to licenses/LICENSE.bootstrap.

[wuchong]

Sure.

[wuchong]

@rmetzger , I removed anchor.min.js because the website can be loaded even without this resource.

[rmetzger]

@rmetzger , I removed anchor.min.js because the website can be loaded even without this resource.

But it seems that we are loading anchor.min.js from a cloudflare CDN.
I would ship the cloudflare files also like bootstrap ourselves.

[wuchong]

@rmetzger I have added back the anchorjs

[rmetzger]

Thanks a lot for fixing this!