query leadership-schedule: add --output-[json,text] flag to control format of the output

[smelc]

Changelog

- description: |
    query leadership: add --output-[json,text] flag to control format of the output. Previous behavior is preserved (write text to stdout, write json to file)
# uncomment types applicable to the change:
  type:
  - feature        # introduces a new feature
  # - breaking       # the API has changed in a breaking way
  - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - improvement    # QoL changes e.g. refactoring
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

• It appears this is a longstanding request from users, as pointed out by @CarlosLopezDeLara to me
• Contributes to fixing [FR] - Make output of CLI commands consistent. #566
• The design is the same as [--output-format json|--output-format json] format becomes [--output-yaml|--output-json] #523 and query utxo: add --output-[json,text] flag to control format of the output #611 to guarantee consistency

How to trust this PR

• I tested this PR manually with this test from cardano-node. I tested all new behaviors.
• I checked manually that the historical behavior was preserved.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff