[website] Update for MXNet 1.8.0 website release

[waytrue17]

Description

Port website release changes from 1.8.0 to master #19988. Also update .htaccess file to redirect to 1.8.0 artifact.

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

• Feature1, tests, (and when applicable, API doc)
• Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

[mxnet-bot]

Hey @waytrue17 , Thanks for submitting the PR
All tests are already queued to run once. If tests fail, you can trigger one or more tests again with the following commands:

• To trigger all jobs: @mxnet-bot run ci [all]
• To trigger specific jobs: @mxnet-bot run ci [job1, job2]

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CI supported jobs: [edge, unix-cpu, windows-cpu, windows-gpu, clang, sanity, website, unix-gpu, miscellaneous, centos-gpu, centos-cpu]

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Note:
Only following 3 categories can trigger CI :PR Author, MXNet Committer, Jenkins Admin.
All CI tests must pass before the PR can be merged.

[waytrue17]

@ys2843 @samskalicky Can you please review?

[samskalicky]

LGTM, thanks!