Allow string values (like "system") in the rowsToScroll schema

[iamakulov]

Summary of the Pull Request

In #3575, Terminal added support for the rowsToScroll field – which accepts integers or "system". However, the settings schema only allows integers:

terminal/doc/cascadia/profiles.schema.json

Lines 289 to 295 in e675de3

	"rowsToScroll": {
	"default": "system",
	"description": "The number of rows to scroll at a time with the mouse wheel. This will override the system setting if the value is not zero or 'system'.",
	"maximum": 999,
	"minimum": 0,
	"type": "integer"
	},

which means writing rowsToScroll: "system" produces the following warning:

This PR fixes the issue.

PR Checklist

• Closes #xxx
• CLA signed. If not, go over here and sign the CLA
• Tests added/passed
• Requires documentation to be updated
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Validation Steps Performed

1. Opened settings and replaced the $schema field with the updated schema from my fork (https://raw.githubusercontent.com/iamakulov/terminal/b5d4c9337d3f323613dd5209bb68decb86cce667/doc/cascadia/profiles.schema.json).
2. Validated that the "system" value doesn’t produce the warning anymore
3. Validated that the value of false (i.e., a boolean – a type that’s not accepted) still produces a warning

[DHowett-MSFT]

thanks!