Disallow Rewards from being enabled and show clearer unavailable messaging for users in unavailable list countries

[Miyayes]

Description

If OS locale country ∈ unavailable list, then:

• Show Rewards unavailable messaging in brave://rewards settings page
• Hide the Rewards NTP widget
• Disable in-line tipping buttons
• Hide BAT icon in the URL bar
• Hide NTPSI-related toggles

For existing users, pause any Rewards services while current OS region country ∈ unavailable list.

Designs: https://www.figma.com/file/ag8i1OV5vpvn4SiOhW2c0f/Github-fixes?node-id=1853%3A34996

Learn more link goes to: https://support.brave.com/hc/en-us/articles/9053832354957

[Miyayes]

cc: @tmancey for the common shared code where this list will live.

[Miyayes]

Unavailable list will come from: #25633

[LaurenWags]

@Miyayes @mkarolin

Looks like a test plan is needed, labelling as QA/Blocked until this is sorted.

cc @kjozwiak @rebron

[LaurenWags]

Per discussion with @Miyayes test plan is under https://github.com/brave/internal/issues/981, verification notes should be added there as well.

cc @brave/qa-team

[GeetaSarvadnya]

Verification PASSED on

Brave | 1.47.161 Chromium: 109.0.5414.61 (Official Build) beta (64-bit)
-- | --
Revision | 846c6eff1c374cde417a9cdc44193545cc07f354-refs/branch-heads/5414@{#1030}
OS | Windows 10 Version 21H2 (Build 19044.2364)

Verification notes can be viewed under https://github.com/brave/internal/issues/981#issuecomment-1369867279.