Add data filters for tags

[MelSumner]

Add filters based on the tags to the violations/index template, so that the content can be filtered appropriately.

• The filters should be a dropdown menu that automatically includes all of the filters.
• The filter should be above the table element
• The tags listed in the dropdown should be alpha-sorted
• the filter/dropdown menu component should itself pass accessibility criteria
• tailwindcss (https://tailwindcss.com/docs) should be used for styling

See https://github.com/dequelabs/combobo (https://dequelabs.github.io/combobo/demo/) for a good example of an accessible combobox for filters. Note the "submit" button.