[Feature]: Contact Requests view: take into account having multiple accounts

[lissine0]

Precondition

• I understood that this template is only for feature requests and not for bug reports

Cross-checked related issues?

• I have cross-checked this overview Overview: Tasks and Issues #322 as well as filtered for related labels https://github.com/monal-im/Monal/labels

Describe your feature

It would be nice if the contact requests view would distinguish which Monal account the requests belong to, in case there are multiple Monal accounts.
A possible way to do it, is grouping all the contact requests belonging to one Monal account together, with the Monal account's address before the grouping.

Currently, it's possible to know this information by clicking the chat icon and seeing the default text in the input box (it shows the relevant Monal account's address)