Preserve empty scopes when generating OpenBao JWT roles

Is this related to a problem? Please describe.

When an OpenBao JWT role is configured with an empty SCOPES value, the migration currently generates [""] instead of an empty array. The current string-based JSON construction can also mishandle quotes and backslashes.

Describe the solution you'd like

Pass the raw scopes value to jq, split non-empty comma-separated values there, and convert an empty value to:

[]

Describe alternatives you've considered

Special-casing empty values and escaping each scope in Bash. Keeping all JSON processing in jq is simpler and safer.

Additional context

Add validation for empty scopes and values containing characters that require JSON escaping. Existing non-empty scope lists must remain unchanged.

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