NetP onboarding: changes a color and updates some assets (#1547)

Task/Issue URL: https://app.asana.com/0/0/1205330979601115/f
- https://app.asana.com/0/0/1205330979601114/f

## Description

Updates some assets according to the design requests in the tasks above.

But in case you want to see more, here's the figma link:
https://www.figma.com/file/nscneJs8hvI6j2m24AFTsD/Setup-steps-macOS-Network-Protection?node-id=176%3A45346&mode=dev

Author: diegoreymendez

LocalPackages/NetworkProtectionUI/Sources/NetworkProtectionUI/Resources/Assets.xcassets/Colors/OnboardingStepBorderColor.colorset/Contents.json

@@ -4,7 +4,7 @@
       "color" : {
         "color-space" : "srgb",
         "components" : {
-          "alpha" : "0.090",
+          "alpha" : "0.180",
           "blue" : "0x00",
           "green" : "0x00",
           "red" : "0x00"
@@ -22,7 +22,7 @@
       "color" : {
         "color-space" : "srgb",
         "components" : {
-          "alpha" : "0.090",
+          "alpha" : "0.180",
           "blue" : "0xFF",
           "green" : "0xFF",
           "red" : "0xFF"

LocalPackages/NetworkProtectionUI/Sources/NetworkProtectionUI/Resources/Assets.xcassets/Icons/apple-vault-icon.imageset/exention-icon.png

@@ -119,7 +119,7 @@ struct OnboardingStepView: View {
         .cornerRadius(8)
         .background(
             RoundedRectangle(cornerRadius: 6, style: .circular)
-                .stroke(Color(.onboardingStepBorder))
+                .stroke(Color(.onboardingStepBorder), lineWidth: 1)
                 .background(
                     RoundedRectangle(cornerRadius: 6, style: .circular)
                         .fill(Color(.onboardingStepBackground))