adding custom "brave://" pages into "brave://about"

[kjozwiak]

Description

We should either create a new brave:// page similar to brave://about that lists custom Brave pages such as brave://local-state, brave://rewards-internals, brave://welcome, brave://adblock and brave://rewards.

Maybe adding a section under brave://about that lists all our current custom pages would also be a good solution.

Steps to Reproduce

1. visit brave://about and notice that none of the custom brave:// pages are listed

Actual result:

Custom brave:// pages are not being listed under brave://about

Expected result:

We should be listing our custom brave:// pages in brave://about

Reproduces how often:

100% reproducible using the STR mentioned above.

Brave version (brave://version info)

Brave	1.1.22 Chromium: 79.0.3945.79 (Official Build) (64-bit)
Revision	29f75ce3f42b007bd80361b0dfcfee3a13ff90b8-refs/branch-heads/3945@{#916}
OS	macOS Version 10.15.1 (Build 19B88)

Version/Channel Information:

• Can you reproduce this issue with the current release? Yes
• Can you reproduce this issue with the beta channel? Yes
• Can you reproduce this issue with the dev channel? Yes
• Can you reproduce this issue with the nightly channel? Yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? N/A
• Does the issue resolve itself when disabling Brave Rewards? N/A
• Is the issue reproducible on the latest version of Chrome? N/A

Miscellaneous Information:

CCing @bsclifton @rebron @brave/legacy_qa