Ledger dApp Staking V3 Promotion Card

[Gunit2481]

Pull Request Summary

Describe what changes this pull request makes to the repository

• Add Ledger dApp Staking V3 banner to dapp_promotions image folder;
• Update dapp_promotions.json file;

Check list

• [ ] contains breaking changes
• [ ] adds new feature
• [ ] modifies existing feature (bug fix or improvements)
• [ ] relies on other tasks
• [ ] documentation changes
• [ ] tested on mobile devices

This pull request makes the following changes:

Adds

• (ex: Add feature A)

Fixes

• (ex: Fix validation function)

Changes

• (ex: Change document B)

To-dos

*Feel free to remove this section if it's not applicable

• [ ] (ex: add user list)