Add `--format json` to `forest-cli chain head`

[LesnyRumcajs]

Summary

Currently, forest-cli chain head produces

❯ forest-cli chain head -n 5
[2097089]
bafy2bzaceajfbzlhuwudsdu3swuhgys2govtyel46akjdbarq2752w7cz7gde
bafy2bzaceapu74bbaxoftc76qbez7vr5a3hmkjcxjfk5pofufwv3wnlk36b3w
bafy2bzaceb2372awzqenvkdgpnkt34ssz64redtf4qb2ewugzbbpekl4kfftq
bafy2bzacebzh3llwhllzxsremaop4u37kbm4quu5bpjiwuoagzgmudmmwsywo
[2097088]
bafy2bzacecxn5fuwwrhanvut4sisoe6ubp64kguhjalmawt6bdqxwvde6n4pe
bafy2bzacebbcf4xzbzfge7hqri3pa2ladnk4urqmlg24nmqdw3v2dzlzu35ia
bafy2bzacebv73y7v42f6nv2rinmfkuoaubmamz5uqsrsp5xe2g6dogsl7uiei
bafy2bzacecmxda677fteaap73ot6pfugcg4ixhsy2axyfnowjxvihg5pf4jds
[2097087]
bafy2bzaceckhkuybrh5uxzubse33kpeyeddzhmt5f3p23myh75c6cr4gnq3jk
bafy2bzacebu7pg2ne3b7tssw4dlf4jmflpid735nwn3rdlqgevzal36o6v5kg
bafy2bzaceblhetqnlhrhedt4hqzypnl4s6kbyqijbklqzl5nqy7euzu4v4qxc
bafy2bzacecwmdjo4zlagcqoqrd47iudkej5z5lzjbunhobxtzyucccjoptldw
[2097086]
bafy2bzaced5nc6tiaa2sada3qee3lveu5jhh45ouec7nwn74fe4nzadkxswg6
bafy2bzacecrna54zlij2gbtzuetliselajexb2nptzqzujdzpggh5wwxwkqq4
bafy2bzacec7iysjbauybb3ooiohgrxqkibuwiqhjno4p5xfqaycc6ur4jvow6
[2097085]
bafy2bzaceae3zvxgzqukg5sznohxozvz3ykf2rnyhthc5zs3lyhy3fneofnvo
bafy2bzacedckvm74g2tsr2vyqgay6xtljwh5xgem66hvri3dy65jmv5mdp6ac
bafy2bzacedat26oxwybmxqxqhzfvn3hspvoknvmgiqr2dvpx7ijagt5ggqu2m

It would be great to have the output also in a programmable form, e.g., JSON.

This holds true for many other subcommands, but let's add those options as needed.

Completion Criteria

• [ ] add --format json as a possible flag to forest-cli chain head that would produce a valid JSON
• [ ] ensure the feature is tested (at least that the JSON is valid)

Additional Links & Resources