fix(opengb): add dedicated error for neon projects exceeded (#847)

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## Changes

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errors/neon/project-limit-exceeded.md

@@ -0,0 +1,9 @@
+---
+name = "NEON_PROJECT_LIMIT_EXCEEDED"
+description = "Neon project limit exceeded."
+http_status = 500
+---
+
+# Neon Project Limit Exceeded
+
+Exceeded the maximum number of neon projects for the global neon account.