ui: clicking the "now" button on db console does not make the graph snap to the frontier

[dhartunian]

When clicking "Now" on the DB Console metrics page, the expected behavior is that the start/end time ranges should be cleared and the graph should snap to the current time frontier and update automatically.

Desired state when clicking "Now":

• If the time picker is set to a custom start/end, we should snap to 10m preset
• If the time picker is already set to a preset, do nothing (since the presets snap to the end of the time frontier)

Currently, when the Metrics page is loaded, we set the start/end times automatically even though the picker is set to the 10m preset. We should instead encode the preset state in the query param to clearly disambiguate between the custom times and the presets.

Jira issue: CRDB-42380

[blathers-crl[bot]]

Hi @dhartunian, please add branch-* labels to identify which branch(es) this C-bug affects.

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