Add custom log attributes API

[tustanivsky]

Native SDK 0.12.2 adds an API for setting custom log attributes which can also be exposed in the Unreal SDK.

Related to:

• https://github-redirect.dependabot.com/getsentry/sentry-native/pull/1435
• https://github-redirect.dependabot.com/getsentry/sentry-native/pull/1450

[linear]

UNREAL-108