Add indices on assets and subtitle field

[jterry64]

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• Bugfix
• Feature
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What is the current behavior?

No index on assets table, no subtitle field. Internal asset queries take up most of the DB time according to New Relic, so want to see if adding an index helps.

Issue Number: GTC-3069

What is the new behavior?

• Indices on dataset and version fields on assets table.
• Subtitle field in metadata

Does this introduce a breaking change?

• Yes
• No

Other information