chore: add links to kubeflow 1.9 manifests

[Al-Pragliola]

This PR updates the "Kubeflow Manifests" section from page "Installing Kubeflow" with the new version and removes the 1.7 one to keep the same number of releases.

1. added links to kubeflow 1.9 manifests
2. removed links to kubeflow 1.7 manifests

[google-oss-prow]

Hi @Al-Pragliola. Thanks for your PR.

I'm waiting for a kubeflow member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[hbelmiro]

/lgtm
/ok-to-test

[rimolive]

/lgtm

[rimolive]

@andreyvelich @terrytangyuan Would you mind approve this? We're updating the installation docs to point to 1.9 as the current release.

[terrytangyuan]

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: terrytangyuan

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