Send pixel on sync secure storage failure (#3542)

Task/Issue URL:
https://app.asana.com/0/414235014887631/1208700858621924/f

**Description**:

This was reviewed here: #3530 and
merged already to the release branch, but there's been conflicts since.
So it needs an extra PR to resolve them.

**Steps to test this PR**:
1. Just make sure this compiles and is pointing to latest BSK release.

**Definition of Done (Internal Only)**:

* [ ] Does this PR satisfy our [Definition of
Done](https://app.asana.com/0/1202500774821704/1207634633537039/f)?

**Copy Testing**:

* [ ] Use of correct apostrophes in new copy, ie `’` rather than `'`

**Orientation Testing**:

* [ ] Portrait
* [ ] Landscape

**Device Testing**:

* [ ] iPhone SE (1st Gen)
* [ ] iPhone 8
* [ ] iPhone X
* [ ] iPhone 14 Pro
* [ ] iPad

**OS Testing**:

* [ ] iOS 15
* [ ] iOS 16
* [ ] iOS 17

**Theme Testing**:

* [ ] Light theme
* [ ] Dark theme

---
###### Internal references:
[Software Engineering
Expectations](https://app.asana.com/0/59792373528535/199064865822552)
[Technical Design
Template](https://app.asana.com/0/59792373528535/184709971311943)

---------

Co-authored-by: Daniel Bernal <[email protected]>

Author: graeme

Core/PixelEvent.swift

@@ -624,6 +624,7 @@ extension Pixel {
         case syncRemoveDeviceError
         case syncDeleteAccountError
         case syncLoginExistingAccountError
+        case syncSecureStorageReadError
 
         case syncGetOtherDevices
         case syncGetOtherDevicesCopy
@@ -1437,6 +1438,7 @@ extension Pixel.Event {
         case .syncRemoveDeviceError: return "m_d_sync_remove_device_error"
         case .syncDeleteAccountError: return "m_d_sync_delete_account_error"
         case .syncLoginExistingAccountError: return "m_d_sync_login_existing_account_error"
+        case .syncSecureStorageReadError: return "m_d_sync_secure_storage_error"
 
         case .syncGetOtherDevices: return "sync_get_other_devices"
         case .syncGetOtherDevicesCopy: return "sync_get_other_devices_copy"

Core/SyncErrorHandler.swift

@@ -100,6 +100,8 @@ public class SyncErrorHandler: EventMapping<SyncError> {
                 Pixel.fire(pixel: .syncFailedToLoadAccount, error: error)
             case .failedToSetupEngine:
                 Pixel.fire(pixel: .syncFailedToSetupEngine, error: error)
+            case .failedToReadSecureStore:
+                Pixel.fire(pixel: .syncSecureStorageReadError, error: error)
             default:
                 // Should this be so generic?
                 let domainEvent = Pixel.Event.syncSentUnauthenticatedRequest