feat(EMS-3826-3829): export contract - agent charges - user flow

[ttbarnes]

Introduction ✏️

This PR updates the "Export contract - agent charges" flow so that it is the same as design:

1. Agent charges form.
2. If FIXED_SUM - Agent charges currency form.
3. Agent FIXED_SUM_AMOUNT form.
4. Check your answers.

Resolution ✔️

• Update E2E tests, commands.
• Update UI POST redirects.
• Remove check/change redirect and alternativeCurrencyUrl logic from AGENT_CHARGES controllers.
• Remove invalid redirects from AGENT_CHARGES_CURRENCY POST controller.

Miscellaneous ➕

• Remove old/unused validation rules.
• Fix a typo.
• Update the HOW_MUCH_IS_THE_AGENT_CHARGING nunjucks template to render a hint.