[Meta] Dashboard dark theme bugs

[bhavyarm]

Meta issue for tracking dashboard darktheme bugs:

• [Clone modal is white on a dark dashboard] ("Clone" modal dialogue is white even though dashboard is dark theme #12988)
• Y Axis line color look bad in dark theme (Y Axis line color look bad in dark theme #12740)
• Can't see legend arrow in dark theme
• Dark theme needed for add filter dialog
• Dark theme panel borders in edit mode
• Dark theme saved search table field value are obscured by filter overlay (Dark theme saved search table field value are obscured by filter overlay #13421)
• Font color for spy panel in dashboard in dark theme is not visible (Font color for spy panel in dashboard in dark theme is not visible. #13325)
• Metric table and mark down font color on dashboard in dark name is not really visible (Metric table and mark down font color on dashboard in dark name is not really visible. #13282)
• Spy panel indicator is not visible in dark mode (Spy panel indicator isn't visible on visualizations when dashboard is in dark theme. #12181)
• Dark theme on dashboard is swallowing up the help text on empty dashboards (Dark theme on dashboard is swallowing up the help text on empty dashboards #12180)

[timroes]

Closing this in favor of: #29417