When override toolchain from toml file is not installed, show a warning

[sdankel]

There should be a warning message indicating that the toolchain from the override file needs to be installed. Currently it just shows "not found" for everything in fuelup show

[alfiedotwtf]

This GitHub Issue currently only talks about fuelup show but I think all tools should be included in the fix...

Here's the output for fuelup show on my machine:

> fuelup show
Default host: aarch64-apple-darwin
fuelup home: /Users/alfie/.fuelup

Installed toolchains
--------------------
beta-3-aarch64-apple-darwin (override)
latest-aarch64-apple-darwin (default)

active toolchain
----------------
beta-3-aarch64-apple-darwin (override), path: /Users/alfie/BACKUP/work/fuellabs/worktrees/counter-contract/master/fuel-toolchain.toml
  forc : 0.37.3
    - forc-client
      - forc-deploy : not found
      - forc-run : not found
    - forc-crypto : not found
    - forc-debug : not found
    - forc-doc : not found
    - forc-fmt : not found
    - forc-lsp : not found
    - forc-tx : not found
    - forc-wallet : 0.2.2
  fuel-core : 0.17.11
  fuel-core-keygen : not found

fuels versions
--------------
forc : 0.39

For me the confusing thing was when jumping straight into forc build:

> forc build
error: Found argument 'build' which wasn't expected, or isn't valid in this context

USAGE:
    forc [OPTIONS] <SUBCOMMAND>

For more information try --help