[Frontend] Show success banner to user when trial starts

What does this MR do?

Part of #13233 (closed).

It will show a success banner/alert to the user when the trial starts, the user will be redirected to the billing page along with trial=true GET parameter.

Showing the banner will depend on the trial parameter and whether the namespace has an active_trial.

Screenshots

User's billing page

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Style guides

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers