Trim whitespace from user input in bootstrap script

Trim user input in bootstrap script.
Example:

First checking for Msys2...

Install MSys2
Do you want GHCup to install a default MSys2 toolchain (recommended)?
[Y] Yes  [N] No  [?] Help (default is "Y"): N
Skipping MSys2 installation.
Input existing MSys2 toolchain directory:
 C:\tools\msys64
MSys2 installation at ' C:\tools\msys64' could not be found!
Input existing MSys2 toolchain directory:
C:\tools\msys64
Setting GHCUP_MSYS2 env var to 'C:\tools\msys64'

A leading space pasted with the directory name caused the script to not find the entered directory.