fix: Output deprecation warning in JSON format when option --json is set

[sfauvel]

Content

This PR outputs client deprecation warning formatted in JSON when the --json option is used

With --json option, the output is:
{"warning": "`snapshot` command is deprecated, use `cardano-db` instead", "type": "deprecation"}

without the option, the output is:
`snapshot` command is deprecated, use `cardano-db` instead

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • CHANGELOG file is updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • No clippy warnings in the CI
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested
• Documentation
  • Update README file (if relevant)
  • Update documentation website (if relevant)
  • Add dev blog post (if relevant)

Issue(s)

Closes #1616

[github-actions]

Test Results

    3 files  ±0     42 suites  ±0   12m 14s ⏱️ + 1m 35s
  914 tests ±0    914 ✅ ±0  0 💤 ±0  0 ❌ ±0 
1 008 runs  ±0  1 008 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit f3c0469. ± Comparison against base commit d3064e6.

♻️ This comment has been updated with latest results.

[jpraynaud]

LGTM 👍