dbt: update text descriptions and allow removing dbt trigger in the UI

[mdibaiee]

Description:

• Made all fields optional in the JSONSchema (although we still check for their existence)
• Updated title and description of interval

Workflow steps:

(How does one use this feature, and how has it changed)

Documentation links affected:

(list any documentation links that you created, or existing ones that you've identified as needing updates, along with a brief description)

Notes for reviewers:

(anything that might help someone review this PR)

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This change is