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

[rebron]

Description

Enable brave://flags/#brave-vertical-tabs as default for Nightly channel

Steps to Reproduce

1. Go to brave://flags/#brave-vertical-tabs and check that it's selected as Default
2. Default value should be enabled.
3. Right click on any tab in horizontal view to see that Vertical tabs option is selected.

Brave version (brave://version info)

1.51.x.

Version/Channel Information:

• Can you reproduce this issue with the current release? n/a
• Can you reproduce this issue with the beta channel? n/a
• 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:

[stephendonner]

@rebron @sangwoo108 looks like we need this enabled on beta channel, too, if we're to test it in 1.51.x: https://github.com/brave/brave-core/pull/17458/files

cc @brave/qa-team and setting as QA/Blocked for now

[LaurenWags]

@stephendonner @rebron we should probably have a separate issue for Beta. Might as well have one for Release too.

[kjozwiak]

Going to label this as QA/No as the verification on beta will be done via #29658 once brave/brave-core#18065 has been uplifted into 1.51.x.