[ads] Follow up to #40507: Add NTP media type p3a metrics

[btlechowski]

Description

Follow up to #40507. When NTT is disabled through brave://rewards, p3a Brave.NTP.SponsoredMediaType is not changed.

Note: changing Brave.NTP.SponsoredMediaType through NTP works as expected

Steps to reproduce

1. Enable rewards
2. Open brave://rewards
3. Turn off NTT
4. Open brave://local-host and search for SponsoredMediaType

Actual result

Brave.NTP.SponsoredMediaType = 1

Expected result

Brave.NTP.SponsoredMediaType = 0

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Brave	1.70.109 Chromium: 128.0.6613.138 (Official Build) beta (64-bit)
Revision	fec4422ae56f4d9680c71a3c1de60b9a8e5ef32f
OS	Linux

cc @tmancey @aseren @iambrianfung

[btlechowski]

Reproduced on Android: Brave v1.70.114 on Lenovo TB-8506FS (Android 11.0)

[LaurenWags]

Requires 1.71.103 or higher for verification 👍🏻

[btlechowski]

Verified on

Brave	1.71.105 Chromium: 129.0.6668.89 (Official Build) beta (64-bit)
Revision	f69ba167992437799f1dbcce81e90ba501a3d63e
OS	Linux

Verified test plan from brave/brave-core#25558

Test case 1

Clean install

Disabled Background images

Enabled Background images

Test case 2

Clean install

Disabled NTT

Enabled NTT

Test case 3

After joining rewards:

Disabled NTT from brave://rewards

Enabled NTT from brave://rewards

[btlechowski]

Verification passed on Brave v1.71.114 on Lenovo TB-8506FS (Android 11.0)

Verified test plan from brave/brave-core#25558

Test case 1

Clean install

Disabled Background images

Enabled Background images

Test case 2

Disabled NTT

Enabled NTT

Test case 3

After joining rewards:

|
--|--|--

Disabled NTT from brave://rewards
|
--|--|--

Enabled NTT from brave://rewards

|
--|--|--