task(payments): Update strings referencing 'Firefox accounts'

Because:
- We want to start the localization effort of updating strings from Firefox to Mozilla

This Commit:
- Creates new l10n strings / ids using the Mozilla branding

packages/fxa-payments-server/src/components/Header/en.ftl

@@ -1,3 +1,4 @@
 ## Component - Header
 
 brand-name-firefox-logo = { -brand-name-firefox } logo
+brand-name-mozilla-logo = { -brand-mozilla } logo

packages/fxa-payments-server/src/components/NewUserEmailForm/en.ftl

@@ -1,6 +1,7 @@
 ## Component - NewUserEmailForm
 
 new-user-sign-in-link = Already have a { -brand-name-firefox } account? <a>Sign in</a>
+new-user-sign-in-link-2 = Already have a { -product-mozilla-account }? <a>Sign in</a>
 # "Required" to indicate that the user must use the checkbox below this text to
 # agree to a payment method's terms of service and privacy notice in order to
 # continue.

packages/fxa-payments-server/src/routes/Checkout/en.ftl

@@ -1,5 +1,6 @@
 ## Routes - Checkout - New user
 
 new-user-step-1 = 1. Create a { -brand-name-firefox } account
+new-user-step-1-2 = 1. Create a { -product-mozilla-account }
 new-user-card-title = Enter your card information
 new-user-submit = Subscribe Now