Implement Buy button link on VPN dialog

[stephendonner]

Description

Implement Buy button link on VPN dialog

Steps to Reproduce

1. install 1.39.92
2. launch Brave
3. open brave://flags
4. set brave://flags/#brave-vpn to Enabled
5. set brave://flags/#skus-sdk to Enabled
6. set brave://flags/#skus-environment to development
7. click on the Relaunch button
8. click on the VPN button on the browser toolbar
9. click on Buy

Actual result:

Nothing happens

Expected result:

Should go to https://account.brave.software/ (in development; account.brave.com in production)

Reproduces how often:

100%

Brave version (brave://version info)

Brave	1.39.92 Chromium: 101.0.4951.54 (Official Build) beta (x86_64)
Revision	67da1aeb32cedd27634ca6634fb79cbd85d3f0ab-refs/branch-heads/4951@{#1126}
OS	macOS Version 11.6.5 (Build 20G527)

cc @nullhook @rebron @mattmcalister @simonhong @brave/qa-team

[GeetaSarvadnya]

++reproduced on windows 10 x64.

[spylogsster]

looks like it as fixed in brave/brave-core#13348

[MadhaviSeelam]

Verification PASSED using

Brave | 1.41.74 Chromium: 103.0.5060.53 (Official Build) beta (64-bit)
-- | --
Revision | a1711811edd74ff1cf2150f36ffa3b0dae40b17f-refs/branch-heads/5060@{#853}
OS | Windows 11 Version 21H2 (Build 22000.739)

Reproduced using original steps in 1.40.100 Chromium: 102.0.5005.125 beta

Confirmed clicking on Buy button loads https://account.brave.software/ when using the development environment in a new tab

Ex1	Ex2	Ex3