Reland "variations: Add a field trial testing config entry for Trust Tokens"

This is a reland of 7d4baea7

Fixed the underlying issue necessitating the revert: crbug.com/1098019.
Ran some of the failing tests locally with setup mimicking the failing
FYI bot's environment and they seem to pass. Unfortunately, I wasn't
able to run the entire failing test suite on a bot with the exact same
setup as the failing FYI bot that prompted the revert.

Original change's description:
> variations: Add a field trial testing config entry for Trust Tokens
>
> We're rolling Trust Tokens (https://bit.ly/trust-token-dd) out so we can
> start its origin trial. (The feature is gated behind both an origin
> trial and a base::Feature; see [1] for a longer description of the
> rollout strategy.)
>
> This CL updates the field trial testing config to enable the
> `TrustTokens` feature with the configuration we're using during the
> rollout.
>
> [1]
> https://groups.google.com/a/chromium.org/g/blink-api-owners-discuss/c/WY17UlZFG3g
>
> R=chromium-metrics-reviews@google.com
>
> Bug: 1036483
> Change-Id: If9cb0611d0f2f236f99918326ce5ee33c991df25
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2255649
> Reviewed-by: Brian White <bcwhite@chromium.org>
> Commit-Queue: Brian White <bcwhite@chromium.org>
> Commit-Queue: David Van Cleve <davidvc@chromium.org>
> Auto-Submit: David Van Cleve <davidvc@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#780881}

Bug: 1036483
Change-Id: I549c6eaff38e019f5d9ca878e2160c0e87b6aee7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2261403Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: David Van Cleve <davidvc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#782105}

testing/variations/fieldtrial_testing_config.json

@@ -6996,6 +6996,28 @@
             ]
         }
     ],
+    "TrustTokenOriginTrial": [
+        {
+            "platforms": [
+                "android",
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "params": {
+                        "TrustTokenOperationsRequiringOriginTrial": "only-issuance-requires-origin-trial"
+                    },
+                    "enable_features": [
+                        "TrustTokens"
+                    ]
+                }
+            ]
+        }
+    ],
     "TrustedTypes": [
         {
             "platforms": [