Fix caddy fmt breaks backquote wrapped braces in template

[keystroke3]

This addresses issue #6859 by writing the opening and closing braces and ignoring indentation when it detects that we the cursor is currently within a backquote section.

I have added 2 new tests for the two cases where the braces are wrapped with regular quotes and backquotes. I have confirmed that it works at least with the following example:

block {
	header Content-Type text/plain
	templates
	respond "Home page date: {{now | date `2006`}}"

	handle /path {
		header Content-Type text/plain
		templates
		respond `Path page date: {{now | date "2006"}}`
	}
}

[CLAassistant]

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[mholt]

Thank you for the patch!