feat(superset/preset): add dataset and column description

[bmaquet]

Add description for datasets and columns

Dataset

• Add a description property to SupersetDataset model.
• Uses the description if it's available, and falls back to empty description if not.

Column

• Uses the description if it's available, and falls back to column name if not.

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Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[bmaquet]

@treff7es small ping for another PR related to superset/preset.
I was waiting for the column-level lineage PR to be merged before I open this one (to prevent merge conflicts).

Thanks a lot in advance for the review!

[yoonhyejin]

Hello @bmaquet -- @treff7es is OOO until this week, so review might be a bit delayed. We’ll aim to take a look next week. Appreciate your patience! 🙂