feat: SubscriptionController: get pricing

[matthiasgeihs]

Explanation

Add a "getPricing" method to the SubscriptionController, which allows the frontend to query the available products and their pricing.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

[chaitanyapotti]

we would need the types for individual items in this as mentioned here to be used in frotend. https://github.com/consensys-vertical-apps/va-mmcx-subscription-api/blob/main/src/subscriptions/dto/pricingDto.ts

Pls type out the same way

[matthiasgeihs]

done