[Proposal] Warn users when duplicate contact names exist in the contact list

### What is this about?

### Purpose 🎯
This proposal aims to handle an edge case for existing contact lists containing duplicate names but different addresses. We should warn users when their contact list contains 2 or more entries with the same name.

### Context 💭
We will soon prevent users from adding contacts if the contact name already exists in their contact list or is one of their reserved account names (see [#26621](https://github.com/MetaMask/metamask-extension/issues/26621)). There should not be 2 separate contact entries with the same name and different addresses.

### Scenario

_No response_

### Design

Suggested Design
The `wallet-ux` team has provided the following design(s) as a starting point - [Figma link](https://www.figma.com/design/IPTpdvQIbHMfisTQFmuo19/Various-Fixes?node-id=435-3&t=riYPG1iHLgGLzq8v-1).


### Technical Details

_No response_

### Threat Modeling Framework

_No response_

### Acceptance Criteria

- A warning should appear If the wallet's contact list contains two or more records with the same name but **different** addresses.

### Stakeholder review needed before the work gets merged

- [x] Engineering (needed in most cases)
- [ ] Design
- [x] Product
- [ ] QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management (please specify)
- [ ] Other (please specify)

### References

### MetaMask Form Validation Design Guidelines
[Figma Link](https://www.figma.com/design/HKpPKij9V3TpsyMV1TpV7C/DS-Components?node-id=21673-8566)