CLI - Warn when using an unstable command

[bfops]

Description of Changes

Addresses #1820.

• Print a warning when using unstable subcommands or args
• Unstable commands also have unstable markers in their --help text

Note: I only added this text to the CLI commands list. I did not add it to other binaries, especially spacetimedb-update.

API and ABI breaking changes

Not API/ABI breaking.

Expected complexity level and risk

1

Testing

• Helptext contains the warning

$ cargo run -pspacetimedb-cli -- init --help
   Compiling spacetimedb-cli v1.0.0-rc4 (/home/lead/work/clockwork-localhd/SpacetimeDBPrivate/public/crates/cli)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 17.35s
     Running `target/debug/spacetimedb-cli init --help`
Initializes a new spacetime project.

WARNING: This command is UNSTABLE and subject to breaking changes.

Usage: spacetimedb-cli init --lang <lang> [project-path]

Arguments:
  [project-path]  The path where we will create the spacetime project [default: .]

Options:
  -l, --lang <lang>  The spacetime module language. [possible values: csharp, rust]
  -h, --help         Print help

• Using an unstable command shows the warning

$ cargo run -pspacetimedb-cli -- list
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.26s
     Running `target/debug/spacetimedb-cli list`
WARNING: This command is UNSTABLE and subject to breaking changes.

Associated database identities for c20058f5a5bbcbfd65110416110492e91d5ab64054640deb456bd5fa8a2ab9d5:

 db_identity                                                      
------------------------------------------------------------------
 c200bff0b7ec3b9af7247886265bc8a831b3f3067b9f32263fcf954d03e98088 
 c200b0e6eda45da7e3c702b2c5e1412517842c34cf06200ed8733551fd624ea0 
 c20001583eb7da147b40500c64d590089c1bb5e112be31eba202c8c50d63baf4 

• Using a subcommand of an unstable command also shows the warning

$ cargo run -pspacetimedb-cli -- server list
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.25s
     Running `target/debug/spacetimedb-cli server list`
WARNING: This command is UNSTABLE and subject to breaking changes.

 DEFAULT  HOSTNAME                           PROTOCOL  NICKNAME              
          foo.com                            https     foo-test-bad-server   
     ***  127.0.0.1:3000                     http      local                 
          testnet.spacetimedb.com            https     testnet               
          foo2.com                           https     foo-test-bad-server-2 
          maincloud.staging.spacetimedb.com  https     maincloud-staging     
          testnet.staging.spacetimedb.com    https     staging   

[cloutiertyler]

This is relevant to #1072

I'm going to remove the release-1.0 label from #1072 because we're marking the command as unstable anyway.

[cloutiertyler]

LGTM now. I think eprintln is the way to go.