Add a gauge metric for current experiments

[yeya24]

Signed-off-by: yeya24 yb532204897@gmail.com

What this PR does / why we need it:

1. Add a gauge metric katib_experiments_current to track the current experiments in the cluster and their status.
2. Add a namespace label in previous counter metrics.

Special notes for your reviewer:

1. Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

Release note:

---

This change is 

[k8s-ci-robot]

Hi @yeya24. 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.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[gaocegege]

/lgtm
/cc @hougangliu

[hougangliu]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hougangliu

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [hougangliu]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[hougangliu]

/ok-to-test