Add NIGHTLY env for Sentry (#5779)

Previously, nightly issue reports and performance transactions were uploaded to 'DEBUG', which may make sense for issues, but not for performance traces.

services/analyticsproviders/sentry/src/main/kotlin/io/element/android/services/analyticsproviders/sentry/SentryAnalyticsProvider.kt

@@ -97,6 +97,6 @@ class SentryAnalyticsProvider(
 
 private fun BuildType.toSentryEnv() = when (this) {
     BuildType.RELEASE -> SentryConfig.ENV_RELEASE
-    BuildType.NIGHTLY,
+    BuildType.NIGHTLY -> SentryConfig.ENV_NIGHTLY
     BuildType.DEBUG -> SentryConfig.ENV_DEBUG
 }

services/analyticsproviders/sentry/src/main/kotlin/io/element/android/services/analyticsproviders/sentry/SentryConfig.kt

@@ -12,5 +12,6 @@ object SentryConfig {
     const val NAME = "Sentry"
     const val DSN = BuildConfig.SENTRY_DSN
     const val ENV_DEBUG = "DEBUG"
+    const val ENV_NIGHTLY = "NIGHTLY"
     const val ENV_RELEASE = "RELEASE"
 }