[JSON] Update JSON field handling

*Copied from [fivetran/dbt_amplitude #24](https://github.com/fivetran/dbt_amplitude/issues/24).*

The following fields are currently treated as JSON-like strings. We need to update their handling to support the new JSON datatype.

| Table | Column | Usage Type | Affects | Comments | Link |
|--------------------|-----------|------------|---------|---------------------------|------|
| account | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__account.sql |
| card | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__card.sql |
| charge | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__charge.sql |
| credit_note | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__credit_note.sql |
| customer | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__customer.sql |
| dispute | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__dispute.sql |
| invoice | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__invoice.sql |
| invoice_line_item | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__invoice_line_item.sql |
| payment_intent | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__payment_intent.sql |
| payment_method | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__payment_method.sql |
| payout | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__payout.sql |
| plan | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__plan.sql |
| price | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__price.sql |
| refund | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__refund.sql |
| subscription | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__subscription.sql |
| transfer | metadata | extract | core | has to be enabled by a var | https://github.com/fivetran/dbt_stripe_source/blob/main/models/stg_stripe__transfer.sql |

Start with the linked models/stg_stripe__account.sql file and compare the metadata handling across the other listed staging models. Trace how these fields are currently represented and identify the project’s existing validation or model checks. Done means all listed metadata fields consistently support the new JSON datatype without breaking the existing variable-controlled extraction.

Written by the indexing model from the issue text.