feat: installer could check if enough space before installing

[eseidel]

A TT tried to install with not enough space. Got a confusing error message.

Receiving objects: 100% (5492/5492), 10.30 MiB | 894.00 KiB/s, done.
Resolving deltas: 100% (1732/1732), done.
Updating files: 100% (6999/6999), done.
HEAD is now at 58dff390 chore: Update engine version to shorebird-3.7.12
Shorebird Engine • revision d470ae25d21f583abe128f7b838476afd5e45bde
Downloading Darwin arm64 Dart SDK from Flutter engine d470ae25d21f583abe128f7b838476afd5e45bde...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100  217M  100  217M    0     0  6542k      0  0:00:34  0:00:34 --:--:-- 9630k
/Users/nils/.shorebird/bin/cache/flutter/bin/cache/dart-sdk/bin/snapshots/dart2js.dart.snapshot:  write error (disk full?).  Continue? (y/n/^C) 
warning:  /Users/nils/.shorebird/bin/cache/flutter/bin/cache/dart-sdk/bin/snapshots/dart2js.dart.snapshot is probably truncated

It appears that the downloaded file is corrupt; please try again.
If this problem persists, please report the problem at:
  https://github.com/flutter/flutter/issues/new?template=1_activation.md

Here is a one liner to get the number of free bytes:
df . | tail -1 | awk '{print $4}'