Feature: opt-in survey when exiting a game

On first start-up, the game will ask if you want to participate
in our automated survey. You have to opt-in, and can easily opt-out
(via the Options) at any time.

When opt-in, whenever you exit a game, a JSON blob will be send
to the survey server hosted by OpenTTD. This JSON blob contains
information that gives a global picture of the game just played:
- What settings were used
- How many humans vs AIs
- How long the game has been played
- Basic information about the OS / CPU

All this information is kept very generic, so there is no
chance we send private information to our survey server.
Nothing in the JSON blob could identify you as a person; it
mostly tells about the game played. At any time you can see
what the JSON blob includes, by pressing the "Preview Survey
Results" button in-game.

.github/workflows/release-windows.yml

@@ -3,6 +3,10 @@ name: Release (Windows)
 on:
   workflow_call:
     inputs:
+      survey_key:
+        required: false
+        type: string
+        default: ""
       is_tag:
         required: true
         type: string
@@ -129,6 +133,7 @@ jobs:
           -DOPTION_USE_NSIS=ON \
           -DHOST_BINARY_DIR=${GITHUB_WORKSPACE}/build-host \
           -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+          -DOPTION_SURVEY_KEY=${{ inputs.survey_key }} \
           -DWINDOWS_CERTIFICATE_COMMON_NAME="${WINDOWS_CERTIFICATE_COMMON_NAME}" \
           # EOF
         echo "::endgroup::"
@@ -153,6 +158,7 @@ jobs:
           -DCMAKE_TOOLCHAIN_FILE="c:\vcpkg\scripts\buildsystems\vcpkg.cmake" \
           -DHOST_BINARY_DIR=${GITHUB_WORKSPACE}/build-host \
           -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+          -DOPTION_SURVEY_KEY=${{ inputs.survey_key }} \
           -DWINDOWS_CERTIFICATE_COMMON_NAME="${WINDOWS_CERTIFICATE_COMMON_NAME}" \
           # EOF
         echo "::endgroup::"