Debug log in ConvertIdentityStoreGroupToAWSGroup prints pointer addresses instead of values

**Describe the bug**

`ConvertIdentityStoreGroupToAWSGroup` (`internal/sync.go`) logs the group id and display name as `*string` pointers, so the debug line prints memory addresses instead of the values:

```go
log.WithField("groupId", group.GroupId).WithField("displayName", group.DisplayName).Debug("ConvertIdentityStoreGroupToAWSGroup() Group converted")
```

`group.GroupId` and `group.DisplayName` are `*string`, so the emitted line looks like:

```
level=debug msg="ConvertIdentityStoreGroupToAWSGroup() Group converted" displayName=0x1400010f810 groupId=0x1400010f7f0
```

**To Reproduce**
Steps to reproduce the behavior:
1. Run ssosync with `--debug` against IAM Identity Center (any sync method that lists groups).
2. Look at the `ConvertIdentityStoreGroupToAWSGroup() Group converted` debug lines.
3. `displayName` and `groupId` show pointer addresses (`0x...`) rather than the group name / id.

**Expected behavior**

The debug line shows the actual values, e.g. `displayName=engineering groupId=9067...-...`, which is what makes the debug output useful when tracing group conversion.

**Additional context**

Version: v2.6.1 (also current master). Both fields are nil-checked immediately above the log call, so dereferencing them (`*group.GroupId`, `*group.DisplayName`) is safe. I'll open a PR with the one-line fix.

Open internal/sync.go and locate ConvertIdentityStoreGroupToAWSGroup, then inspect the nil checks immediately before the debug log. Run ssosync with --debug against IAM Identity Center and confirm the conversion log shows the group name and ID values rather than pointer addresses.

Written by the indexing model from the issue text.