feat: add JSON output to server members command

[farbodahm]

This pr is related to #15894.

Now we can pass -json argument to nomad server members command to get the output in JSON format.
It works both for Normal view and Verbose view.

Also related tests are added and documentation is here: website/content/docs/commands/server/members.mdx.

Please let me know if anything is needed.

[farbodahm]

@tgross Hey man, is there any update about this PR?
Think of this just as a reminder message and saying that I will be happy if I can help with any part.
Thanks.

[jrasell]

Hi @farbodahm and thanks for raising this PR! Apologies we didn't get to this sooner.

A member of the engineering team was also working on this addition which has been raised as a PR within #16444. Our commands are a little weird in the fact that the -json flag will output the entire object and not adhere to other flags such as -verbose. These are used to control the structured output only; again I realise this is a little unnatural, however, keeping consistency across the commands is important. It also keeps the implementation simpler, as you can see from the linked PR.

I am therefore going to suggest we take the newer PR and close this out without merging. Again, we are sorry this fell through our triage process and ended up conflicting with another PR. Please let me know if you have any questions or other comments.

[farbodahm]

Thanks for mentioning this @jrasell.
Now by saying this, it also makes sense for me. Feel free to continue with the other PR and please let me know if anything else is needed.
Thanks.