Hparams: Avoid retrieving metrics when populating timeseries runs table with hparams.

[bmd3k]

The runs table does not display any of the metric fields/data returned by the hparams plugin. We want to avoid unnecessarily calculating this data on the backend.

The hparams plugin allows requests to specify an include_metrics parameter (added in #6556). We set this flag to false for all hparams-related requests coming from the "hparams_data_source".

Testing:

• Observed in both OSS and internal TensorBoard that setting this flag to False results in responses that do not include the metric data.
• Observed that hparams in timeseries runs table still works.
• Observed that hparams in experiment list runs table still works.