add --output-document to multisign-batch

[alessio]

Closes: #8870

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #8873 (452e6ac) into master (c6af0ed) will increase coverage by 0.00%.
The diff coverage is 60.00%.

@@           Coverage Diff           @@
##           master    #8873   +/-   ##
=======================================
  Coverage   59.15%   59.15%           
=======================================
  Files         570      570           
  Lines       31770    31774    +4     
=======================================
+ Hits        18793    18797    +4     
+ Misses      10776    10775    -1     
- Partials     2201     2202    +1     

Impacted Files	Coverage Δ
server/test_helpers.go	0.00% <0.00%> (ø)
x/auth/client/cli/tx_multisign.go	64.88% <71.42%> (+0.04%)	⬆️
x/auth/client/cli/tx_sign.go	74.59% <100.00%> (ø)

[orijbot]

Benchmark beginning. Status page: https://github.orijtech.com/benchmark/status?commit=69f66e4abde3f2aaf5bd250051783cff6b93ba66

[orijbot]

Benchmark finished. See the result: https://github.orijtech.com/benchmark/result?id=f093bc9852f94b919275ae2ffd14479b

[orijbot]

Benchmark beginning. Status page: https://github.orijtech.com/benchmark/status?commit=452e6acbef2a435f041b28dcd1449e5291bfdefe