Disclosing import match rules

[fhreichert]

Is your feature request related to a problem? Please describe.
When importing, great care is needed to prevent duplicate external accounts.

Describe the solution you'd like
An indication that allows me to identify if an imported transaction account has been matched (either by exact matching or replacement rule. Ideally, there is sufficient information for the type of match and the match rule, to discern, how the match was made)

[morremeyer]

The backend portion of this is implemented in #737, I created a follow-up issue in the frontend: envelope-zero/frontend#1023

Please watch the frontend issue for further updates.