Add "ads enabled" pref in local state replicating setting of last loaded profile

[DJAndries]

Add an "ads enabled" pref in local state which replicates the enabled setting of the last loaded profile, so that the stats updater can retrieve the setting without having to depend on the profile.

Remove the profile observer and any calls to the ProfileManager from the stats updater (should fix #4599).

[btlechowski]

Verification passed on

Brave	1.49.91 Chromium: 110.0.5481.77 (Official Build) beta (64-bit)
Revision	65ed616c6e8ee3fe0ad64fe83796c020644d42af-refs/branch-heads/5481@{#839}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#16026

single profile - ads enabled

brave.brave_ads.enabled_last_profile: true

Usage ping:

https://laptop-updates.brave.com/1/usage/brave-core?platform=linux-bc&channel=beta&version=1.49.110&daily=true&weekly=false&monthly=false&first=false&woi=2023-02-27&dtoi=2023-03-01&ref=BRV001&adsEnabled=true&arch=x86_64&wallet2=0

single profile - ads disabled

brave.brave_ads.enabled_last_profile: false

Usage ping:

https://laptop-updates.brave.com/1/usage/brave-core?platform=linux-bc&channel=beta&version=1.49.110&daily=true&weekly=false&monthly=false&first=false&woi=2023-02-27&dtoi=2023-03-01&ref=BRV001&adsEnabled=false&arch=&wallet2=0

profile 1: ads enabled, profile 2: ads disabled, profile 1 active

brave.brave_ads.enabled_last_profile: true

Usage ping:

https://laptop-updates.brave.com/1/usage/brave-core?platform=linux-bc&channel=beta&version=1.49.110&daily=true&weekly=false&monthly=false&first=false&woi=2023-02-27&dtoi=2023-03-03&ref=BRV001&adsEnabled=true&arch=x86_64&wallet2=0

profile 1: ads enabled, profile 2: ads disabled, profile 2 active

brave.brave_ads.enabled_last_profile: false

Usage ping:

https://laptop-updates.brave.com/1/usage/brave-core?platform=linux-bc&channel=beta&version=1.49.110&daily=true&weekly=false&monthly=false&first=false&woi=2023-02-27&dtoi=2023-03-03&ref=BRV001&adsEnabled=false&arch=&wallet2=0

[btlechowski]

Verification passed on Brave v1.49.108 on Lenovo TB-8506FS (Android 11.0)

Verified test plan from brave/brave-core#16026

There are no profiles on Android so the test was limited to one profile

single profile - ads enabled

Usage ping:

https://laptop-updates.brave.com/1/usage/brave-core?platform=android-bc&channel=beta&version=1.49.108&daily=true&weekly=false&monthly=false&first=false&woi=2023-02-27&dtoi=2023-03-02&ref=BRV001&adsEnabled=true&arch=aarch64&wallet2=0

single profile - ads disabled

Usage ping:

https://laptop-updates.brave.com/1/usage/brave-core?platform=android-bc&channel=beta&version=1.49.108&daily=true&weekly=false&monthly=false&first=false&woi=2023-02-27&dtoi=2023-03-02&ref=BRV001&adsEnabled=false&arch=aarch64&wallet2=0