Fix DORA metric Graphql type

What does this MR do and why?

Some DORA metrics can be float so we need float data type. REST API returns float, while GraphQL had "Int" data type. Here we make GraphQL type to be float too.

Usually changing response field type is a breaking change, but I think changing int to float should not cause any issue as a float to int is convertible in most of the languages.

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