SSH Agent Integration (#334)

Hook into an existing SSH Agent.
This allows us to pull keys already authenticated by the agent and write
to the agent ourselves.

---------

Co-authored-by: Evan Simkowitz <esimkowitz@users.noreply.github.com>

pkg/trimquotes/trimquotes.go

@@ -0,0 +1,28 @@
+package trimquotes
+
+import (
+	"strconv"
+)
+
+func TrimQuotes(s string) (string, bool) {
+	if len(s) > 2 && s[0] == '"' {
+		trimmed, err := strconv.Unquote(s)
+		if err != nil {
+			return s, false
+		}
+		return trimmed, true
+	}
+	return s, false
+}
+
+func TryTrimQuotes(s string) string {
+	trimmed, _ := TrimQuotes(s)
+	return trimmed
+}
+
+func ReplaceQuotes(s string, shouldReplace bool) string {
+	if shouldReplace {
+		return strconv.Quote(s)
+	}
+	return s
+}