tpl/strings: Add TrimSpace function

[jmooring]

Use https://pkg.go.dev/strings#TrimSpace so we can do this:

{{ $v | strings.TrimSpace }}

Instead of this:

{{ strings.Trim $v "\n\r " }}

In addition to having a standard definition of white space, we can pipe values into strings.TrimSpace. We can't pipe values into strings.Trim.