Auto-generate ArangoDBErrors.cs

[tjoubert]

Create a script that updates ArangoDBErrors.cs automatically, so that we can easily update it between ArangoDB releases.

[DiscoPYF]

We now have a semi-automated way of updating the enum file: https://github.com/ArangoDB-Community/arangodb-net-standard/blob/master/contributing.md#generating-enum-for-error-codes

1. Copy the list of codes from https://docs.arangodb.com/stable/develop/error-codes-and-meanings/ into a file.
2. Build and run ErrorEnumGenerator with the file as the first argument.
3. Replace existing ArangoDBErrors.cs with the generate one.