Enable bitFlyer by default (uplift to 1.25.x)

[brave-builds]

Uplift of #8712
Resolves brave/brave-browser#15631

Pre-approval checklist:

• You have tested your change on Nightly.
• This contains text which needs to be translated.
  • There are more than 7 days before the release.
  • I've notified folks in #l10n on Slack that translations are needed.
• The PR milestones match the branch they are landing to.

Pre-merge checklist:

• You have checked CI and the builds, lint, and tests all pass or are not related to your PR.

Post-merge checklist:

• The associated issue milestone is set to the smallest version that the changes is landed on.

[kjozwiak]

test-browser failed on post-init as per https://ci.brave.com/job/pr-brave-browser-pr8712_ksmith-enable-bitflyer_1.25.x-linux/1/testReport. However, I'm going to restart as it only takes ~30min for post-init to pass.

linux / test-browser / RewardsContributionBrowserTest.AutoContributionMultiplePublishersUphold
linux / test-browser / RewardsNotificationBrowserTest.InsufficientNotificationForACNotEnoughFunds

test-browser failed on Linux as per https://ci.brave.com/job/pr-brave-browser-pr8712_ksmith-enable-bitflyer_1.25.x-linux/1/testReport. However, these are known intermittent failures and unrelated to this specific PR.

linux / test-browser / RewardsContributionBrowserTest.AutoContributionMultiplePublishersUphold
linux / test-browser / RewardsNotificationBrowserTest.InsufficientNotificationForACNotEnoughFunds

[kjozwiak]

post-init failed due to audit-deps warnings as per https://ci.brave.com/job/pr-brave-browser-pr8712_ksmith-enable-bitflyer_1.25.x-post-init/3/execution/node/144/log/. However, these are unrelated to this specific PR.

[kjozwiak]

Uplift into 1.25.x approved after deliberating with @brave/uplift-approvers.