Changes to multivariate feature variation values not recorded in audit log

### How are you running Flagsmith

- [ ] Self Hosted with Docker
- [ ] Self Hosted with Kubernetes
- [X] SaaS at flagsmith.com
- [ ] Some other way (add details in description below)

### Describe the bug

The following changes to multivariate features are recorded to the audit log correctly:

* Enabled/disabled state
* Control value (recorded as "Remote config value updated", which is technically correct but misleading)
* Segment override changes

However, changes to variation values themselves are not recorded in the audit log. Variation values are equally important as the control value and need to be tracked for audit purposes in the same way.

Changes to variation weights are recorded, but the audit log entries only show the modified weight and not the actual variation that was changed, which is far more important.

### Steps To Reproduce

1. Create a multivariate feature
2. Update any variation value or weights, or add a new variation

Changes to variation values are not saved to the audit log.

Changes to variation weights do not show which variation it applies to.

Entries are created for new variations, but there are no details saved about the new variations or their weights.

### Expected behavior

All changes or additions to multivariate features should be recorded to the audit log.

### Screenshots

"Variation added" does not show which variation was added or its weight:


"Weight changed" does not show which variation this applies to:


"Variation value updated" does not create an entry:

https://github.com/Flagsmith/flagsmith/assets/829698/84df25c1-e528-4fc8-85c1-814c6ed07644