[MultiTypeBlockMatrix] Implement frobenius_norm()

(cherry picked from commit 46cc7dce)

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• cf3891f6 - Mention new methods in MultiTypeBlockMatrix

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• 9b6c149c - Fetch default yml files via different project instead of url

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• 877d39e3 - Fetch default yml files via different project instead of url

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mentioned in commit 3f96dfcc

merged