Option to treat Alphanumeric sender ID as known contact

[sudoshindo]

Checklist

• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
• This issue contains only one feature request.
• I have read and understood the contribution guidelines.
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Feature description

Quick side note: This is related to item #2 on the checklist, I have a previous issue about this, someone just marked it as invalid and refused to hear me out on why it's a valid concern.

#187

Why do you want this feature?

Major companies/services and even government institutions in several countries tend to use these sender IDs to send important service announcements or even OTPs (one-time pins/passwords).

I UNDERSTAND THAT "Block messages from not stored contacts" IS WORKING CORRECTLY. But having this fine grained control may be necessary for a lot of people who regularly interact with services that have these IDs.

Additional information

Possible Compromise:

From issue #187

Also I don't see a way to add these IDs to your contacts as a workaround. The app hides the Add Contact button for threads involving these senders.

You can add to contacts by long pressing the thread on the conversation list.

I suggest making this more obvious by keeping the Add Contact icon visible on the top right of a conversation/thread.

In the current version of the app, the top right icons are: trash icon, call icon, add contact icon, 3 dot menu

On an alphanumeric sender ID, the icons change to: trash icon, archive icon, 3 dot menu

Just consistently show the add contact icon to make it obvious and avoid confusion.