Add a setting to turn off the warning if 'Touch Keyboard and
Handwriting Panel Service' is disabled.
The service might not start in some case, and it doesn't affect the
input in some computer. This PR turn off the warning even if the
service is disabled. The setting name is "inputServiceWarning".
## Validation Steps Performed
I manually set the service to "Disabled", restarted the Terminal,
verified the warning up, then set "inputServiceWarning" to false and
restarted the Terminal, and the warning didn't appear.
References #8095
References https://github.com/microsoft/terminal/issues/7886#issuecomment-729350169
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