Currently, the vast majority of our `fxa_reg - complete` events in
Amplitude are incorrectly showing up with `utm_source` set to `email`.
This is because the auth server forces it on all links in email
addresses, so when the user clicks the verification link the original
`utm_source` for that flow is overwritten.
A separate PR for the auth server [1] has been opened to prevent this
from happening. But in order for that PR not to break legitimate cases
where we want `utm_source` set to `email`, we must first handle those
legitimate cases elsewhere. Hence this PR.
The connect-another-device view can only be reached from a verification
email. When a user signs in from that view, we always want the new flow
to have `utm_source` set to `email`. This change simply hard-codes the
`utm_source` on signin links in that view.
Related issues:
  * #6258
  * mozilla/fxa-auth-server#2496
[1]: mozilla/fxa-auth-server#2505

Currently, the vast majority of our `fxa_reg - complete` events in
Amplitude are incorrectly showing up with `utm_source` set to `email`.
This is because the auth server forces it on all links in email
addresses, so when the user clicks the verification link the original
`utm_source` for that flow is overwritten.
A separate PR for the auth server [1] has been opened to prevent this
from happening. But in order for that PR not to break legitimate cases
where we want `utm_source` set to `email`, we must first handle those
legitimate cases elsewhere. Hence this PR.
The connect-another-device view can only be reached from a verification
email. When a user signs in from that view, we always want the new flow
to have `utm_source` set to `email`. This change simply hard-codes the
`utm_source` on signin links in that view.
[1]: mozilla/fxa-auth-server#2505
Related issues:
  * #6258
  * mozilla/fxa-auth-server#2496
#6342
r=shane-tomlinson