Add instrumentation around currency conversion and fiat/crypto toggle usage settings

### What is this about?

We’re looking to update the fiat aggregated balance UX but need to understand how users use some of the settings around that number. We need to collect telemetry to help us make more data driven decisions.

A/C:

collect usage data on # of users with ETH vs Fiat toggle

collect usage data on which currency users select with currency conversion selection

### Scenario

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### Design

_No response_

### Technical Details

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### Threat Modeling Framework

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### Acceptance Criteria

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### Stakeholder review needed before the work gets merged

- [X] Engineering (needed in most cases)
- [ ] Design
- [ ] 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

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Start by locating the mobile screens or components that contain the ETH-versus-fiat toggle and currency conversion selection. Determine the existing telemetry pattern before defining events for toggle usage and selected currencies; done means both usage measurements are collected as described in the acceptance criteria.

Written by the indexing model from the issue text.