Update UserActivity study defaults to match the Griffin seed

[tmancey]

        {
            "name": "BraveAds.UserActivityStudy",
            "experiments": [
                {
                    "name": "Triggers=NTPSI/TimeWindow=15m/Threshold=0.0/IdleTimeThreshold=5s",
                    "probability_weight": 100,
                    "parameters": [
                        {
                            "name": "triggers",
                            "value": "0D0B14110D0B14110D0B14110D0B1411=-1.0;0D0B1411070707=-1.0;07070707=-1.0"
                        },
                        {
                            "name": "time_window",
                            "value": "15m"
                        },
                        {
                            "name": "threshold",
                            "value": "0.0"
                        },
                        {
                            "name": "idle_time_threshold",
                            "value": "5s"
                        }
                    ],
                    "feature_association": {
                        "enable_feature": ["UserActivity"]
                    }
                },
                {
                    "name": "Default",
                    "probability_weight": 0
                }
            ],
            "filter": {
                "channel": ["NIGHTLY", "BETA", "RELEASE"],
                "platform": ["WINDOWS", "MAC", "LINUX", "ANDROID"]
            }
        },

[tmancey]

Before deprecating studies where the feature is enabled by default we should ensure that all users, especially Android users, have proper feature values in the code across all platforms. If the feature is disabled by default then we should test that the default values are working as expected

[btlechowski]

Verification passed on

Brave	1.46.83 Chromium: 107.0.5304.68 (Official Build) beta (64-bit)
Revision	a4e93e89d3b3df1be22214603fba846ad0183ca5-refs/branch-heads/5304@{#991}
OS	Ubuntu 18.04 LTS

Verified default values for User Activity are:

threshold = 0
time window = 15 minute

[2437:2437:1030/234115.718716:VERBOSE6:user_activity_manager.cc(49)] Triggered event: 02 (0:0:900 s)

Idle Time Threshold = 5 seconds

[2437:2437:1030/234355.946093:VERBOSE1:browser_manager.cc(138)] Browser did enter foreground
[2437:2437:1030/234355.946332:VERBOSE6:user_activity_manager.cc(49)] Triggered event: 01 (0:0:900 s)
[2437:2437:1030/234402.110286:VERBOSE1:idle_detection_manager.cc(66)] User is idle
[2437:2437:1030/234403.148564:VERBOSE1:idle_detection_manager.cc(56)] User is active after 5 s