Add indices on assets and subtitle field

[jterry64]

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• Make sure you are requesting to pull a topic/feature/bugfix branch (right side). Don't request your master!
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Pull request type

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• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Internal calls to the asset table take up most of our DB time

Issue Number: GTC-3069

What is the new behavior?

• Create index on assets on table on dataset and version
• Add subtitle field to metadata

Does this introduce a breaking change?

• Yes
• No

Other information