Enable brave://flags/#brave-vertical-tabs in Beta channel

[stephendonner]

Description

Enable brave://flags/#brave-vertical-tabs in Beta channel

(We set it for Nightly over in #28872.)

Steps to Reproduce

1. install latest beta build
2. launch Brave
3. load brave://flags
4. confirm that brave://flags/#brave-vertical-tabs is set to Default
5. load a few tabs
6. context-click a tab
7. look for the option to Use Vertical Tabs

Actual result:

Not present

Expected result:

brave://flags/#brave-vertical-tabs should be set internally to Enabled, making Use Vertical Tabs available as a toggle on tabs

Reproduces how often:

100%

Brave version (brave://version info)

Brave	1.51.86 Chromium: 112.0.5615.49 (Official Build) beta (x86_64)
Revision	bd2a7bcb881c11e8cfe3078709382934e3916914-refs/branch-heads/5615@{#936}
OS	macOS Version 11.7.6 (Build 20G1231)

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 nightly channel? No

Other Additional Information:

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

Miscellaneous Information:

/cc @rebron @sangwoo108 @brave/qa-team

[kjozwiak]

The above requires 1.51.96 or higher for 1.51.x verification 👍

[stephendonner]

Verified PASSED using

Brave	1.51.96 Chromium: 112.0.5615.121 (Official Build) beta (x86_64)
Revision	39cc4e45904ae9f1741c4fbaa866e629c96f2268-refs/branch-heads/5615_51@{#8}
OS	macOS Version 13.4 (Build 22F5037d)

Steps:

1. installed 1.51.96
2. launched Brave
3. opened brave://flags
4. confirmed Default value for brave://flags/#brave-vertical-tabs
5. context-clicked the tab
6. chose Use Vertical Tabs
7. confirmed new vertical-tab layout
8. loaded brave.com
9. context-clicked the tab

Confirmed context-menu items and defaults for vertical tab were correct

brave://flags	Use Vertical Tabs	context-menu options