Add instructions to use ngrok for migration testing (#25420)

Adding some capabilities to test migration locally with ngrok. To test
HTTPS.

tools/tuf/test/migration/README.md

@@ -1,6 +1,7 @@
 # `migration_test.sh`
 
 This script is used to test the migration from one local TUF repository to a new local TUF repository (with new roots).
+The "old" TUF will be hosted on port 8081, and the new TUF will be hosted on port 8082.
 
 > Currently supports running on macOS only.
 
@@ -15,7 +16,19 @@ LINUX_HOST_HOSTNAME=foobar-ubuntu \
 ./tools/tuf/test/migration/migration_test.sh
 ```
 
-To simulate an outage of the TUF during the migration run the above with:
+To test TUFs with HTTPS instead of HTTP with two ngrok tunnels that connect to 8081/8082:
+```sh
+OLD_TUF_URL=https://121e9b4a4dab.ngrok.app \
+NEW_TUF_URL=https://12oe8b5b3cc6.ngrok.app \
+```
+
+To simulate an outage of the new TUF server during the migration run the above with:
+```sh
+SIMULATE_NEW_TUF_OUTAGE=1 \
+```
+
+To simulate an outage of the new TUF server during the migration and a "need" to patch orbit on the old repository:
 ```sh
 SIMULATE_NEW_TUF_OUTAGE=1 \
+ORBIT_PATCH_IN_OLD_TUF=1 \
 ```

tools/tuf/test/migration/migration_test.sh

@@ -51,13 +51,21 @@ sudo orbit/tools/cleanup/cleanup_macos.sh
 prompt "Please manually uninstall fleetd from $WINDOWS_HOST_HOSTNAME and $LINUX_HOST_HOSTNAME."
 
 OLD_TUF_PORT=8081
-OLD_TUF_URL=http://host.docker.internal:$OLD_TUF_PORT
+if [ -z "$OLD_TUF_URL" ]; then
+	OLD_TUF_URL=http://host.docker.internal:$OLD_TUF_PORT
+else
+	echo "Using the provided URL '$OLD_TUF_URL' for the old TUF server"
+fi
 OLD_TUF_PATH=test_tuf_old
 OLD_FULL_VERSION=1.37.0
 OLD_MINOR_VERSION=1.37
 
 NEW_TUF_PORT=8082
-NEW_TUF_URL=http://host.docker.internal:$NEW_TUF_PORT
+if [ -z "$NEW_TUF_URL" ]; then
+	NEW_TUF_URL=http://host.docker.internal:$NEW_TUF_PORT
+else
+	echo "Using the provided URL '$NEW_TUF_URL' for the new TUF server"
+fi
 NEW_TUF_PATH=test_tuf_new
 NEW_FULL_VERSION=1.38.0
 NEW_MINOR_VERSION=1.38