Allow auto-select for stackID when only finding one stack

[tomasmik]

➜  empty git:(diff) ✗ /Users/tomas/spacelift-io/spacectl/build/aa stack show
Enable auto-selection by setting SPACECTL_SKIP_STACK_PROMPT=true
Use the arrow keys to navigate: ↓ ↑ → ←  and / toggles search
? Found 1 stacks, select one:
  ▸ doublestack
2024/09/27 14:49:35 ^C
➜  empty git:(diff) ✗ SPACECTL_SKIP_STACK_PROMPT=true
➜  empty git:(diff) ✗ /Users/tomas/spacelift-io/spacectl/build/aa stack show

Provider   | GitHub
Repository | empty
Branch     | master

closes: https://github.com/spacelift-io/spacectl/issues/259