[#892] Add `MichelsonFailedCustom` to `MichelsonFailed`

Description

Problem: In morley-debugger, there is a case where we want to throw a custom error that doesn't exist in MichelsonFailed. We should add a new constructor for handling custom failure.

Solution: Add MichelsonFailedCustom, fix haddock comments.

Related issue(s)

Resolves #892 (closed)

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