add "distribution name" notice on "installing kubeflow" + style improvements

[thesuperzapper]

The changes in this PR:

• The main purpose of this PR is to add a warning that says Kubeflow on <PLATFORM> is just name, and not the only way to install Kubeflow on that platform.
• We also update the "header colors" of the tables, to look nicer.
• We also update the text above each table to be more correct.
• We also updated the text for the "raw manifests", to better explain that using them requires "manual patches of YAML".

After we merge this, we need to move the Kubeflow on AWS distribution to the legacy distribution table, there is an existing PR to do this:

• https://github.com/kubeflow/website/pull/3641

Screenshot

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[thesuperzapper]

@zijianjoy can review this and approve if you think it's an improvement.

I think it's an important change, because right now, users are confused about the Kubeflow on XXXX distributions, and this PR adds a notice that tells users that these are not "official" from Kubeflow's perspective, they are just their names.

[jbottum]

I am supportive of the additional language on distribution names. On the other changes, I am questioning if the community has agreed on the 6 month rule to define legacy distributions. This seems like a policy that needs to be agreed upon before making web site updates.

[thesuperzapper]

@jbottum the main feedback from the community call was about the wording of the "distribution name notice", based on that, I have updated it to say "not the only", rather than "not the official":

Also, regarding the 6-month rule, let's discuss that in a separate change, because that wording is currently on the website, and the other changes from this PR are very helpful to new users.

If we are happy with the change I would love to get this merged, so people know that "Kubeflow on AWS" is not the only way to use Kubeflow on AWS (especially now that "Kubeflow on AWS" is no longer maintained).

[jbottum]

I am ok with these changes

[thesuperzapper]

@andreyvelich based on your comments in the meeting today, I pushed a small update to the PR with the following changes:

1. Added "What is Kubeflow?" to before the Kubeflow introduction at the top
   • Linked the "Introduction" and "Architecture" pages more clearly at the top.
2. Updated the information in the "Raw Kubeflow Manifests":
   • Now links directly to the specific v1.8.0 release tags in kubeflow/manifests rather than linking people to master (which may not be installable at any specific time).

[andreyvelich]

I think, we can merge this PR given our discussions in https://github.com/kubeflow/website/pull/3643#discussion_r1499312788 and https://github.com/kubeflow/website/pull/3643#discussion_r1496665276 /lgtm /assign @kubeflow/kubeflow-steering-committee @juliusvonkohout @james-jwu @zijianjoy

[thesuperzapper]

@zijianjoy @james-jwu because this updates the CSS stylesheet, we need a root approver.

This PR should be ready to merge now, if you approve.

NOTE: the DOC check is not actually marked as "required", so it can be merged if approved.

[andreyvelich]

/hold due to https://github.com/kubeflow/website/pull/3693

[thesuperzapper]

Closing because we merged https://github.com/kubeflow/website/pull/3693