Elevate 'Time Series' dashboard as first dashboard - tracking and feedback

This issue is to track work and collect pre-release feedback as we elevate the 'Time Series' dashboard to be the first dashboard in TensorBoard.

With https://github.com/tensorflow/tensorboard/pull/5698 we will be elevating the 'Time Series' dashboard to be the first dashboard in TensorBoard. It will be available in our nightlies and then be part of the the next minor TensorBoard release (2.10.0).

What is the 'Time Series' dashboard?

The 'Time Series' dashboard is a new, unified, view of scalars, histograms, and images data. It has been available for some time but is generally the last dashboard listed in the TensorBoard header. After quite a bit of work improving it and using it internally at Google, we've decided it is time to elevate it to be the first dashboard.

This means that if you've previously seen the 'Scalars', 'Images', or 'Histograms' dashboards as the default dashboard, you will now see the 'Time Series' dashboard as the default dashboard instead. Those other dashboards are still available and can be selected from the TensorBoard header.

See the Time Series README for a bit more information.

Feedback

Feedback can be provided by replying to this issue or opening a new issue.

Start with PR 5698 and tensorboard/plugins/metrics/README.md to understand the Time Series dashboard and its elevation in TensorBoard. Review the pre-release behavior and feedback in this issue; completion is not defined as a self-contained code change, since the issue tracks release rollout and collects reports.