Improve gitleaks setup

This accomplishes a few things:
1. Removes some entries in .gitleaksignore which were incorrect (the
   commit hash did not match the commit that introduced the change)
2. Moves our handling of the debug google services file to a gitleaks
   config file. That means that no matter where that secret shows up, it
   will be allowed (as opposed to handling it in the gitleaksignore file
   which required specifying every location/commit where the secret was
   introduced).
3. Adds the old IntentUtilTest example api key to the list of ignored
   secrets so that it does not get flagged up when running `gitleaks detect`.

.gitleaks.toml

@@ -0,0 +1,8 @@
+[extend]
+useDefault = true
+
+[allowlist]
+description = "global allow list"
+regexes = [
+    "AIzaSyBguqVfwriVWjnSqRg50XPfZZH5r1VumNM",
+]

.gitleaksignore

@@ -1,5 +1,4 @@
-e1cea16b77b1e331bfa8c5a8135dcdf24f32cf6f:app/google-services.json_debug-only:gcp-api-key:23
-e306375a06498977fa176519a0c4a5d463bb47bf:app/src/debugProd/google-services.json:gcp-api-key:23
-e306375a06498977fa176519a0c4a5d463bb47bf:app/src/debugProd/google-services.json:gcp-api-key:23
-e1cea16b77b1e331bfa8c5a8135dcdf24f32cf6f:automotive/google-services.json_debug-only:gcp-api-key:23
-28aab01a878ce90aa6202af6124e120524e3bfc8:wear/google-services.json_debug-only:gcp-api-key:23
+d1502d9bf89fec3e19098f3ec78bc41e1473b447:app/src/androidTest/java/au/com/shiftyjelly/pocketcasts/views/helper/IntentUtilTest.kt:generic-api-key:29
+d1502d9bf89fec3e19098f3ec78bc41e1473b447:app/src/androidTest/java/au/com/shiftyjelly/pocketcasts/views/helper/IntentUtilTest.kt:generic-api-key:33
+d1502d9bf89fec3e19098f3ec78bc41e1473b447:app/src/androidTest/java/au/com/shiftyjelly/pocketcasts/views/helper/IntentUtilTest.kt:generic-api-key:49
+d1502d9bf89fec3e19098f3ec78bc41e1473b447:app/src/androidTest/java/au/com/shiftyjelly/pocketcasts/views/helper/IntentUtilTest.kt:generic-api-key:53