Add option to use emoji for collection icons

[tommoor]

Related #6469 and #2356

Should be relatively straight forward, all the pieces exist.

[linear]

OLN-236 Add option to use emoji for collection icons

[hmacr]

Couple of approaches to solve this.

1. Re-use the icon column and store the emoji. When displaying the collection info, check the collection-icons; otherwise fallback to emoji.
2. Create a new column emoji. At any point, either icon (or) emoji is set for a collection.

I recommend #2 as it gives a cleaner separation between built-in icons and emojis.
@tommoor Your thoughts?

[tommoor]

I think actually (1) is preferable, using the same column. It is easy to differentiate between an emoji and an icon, there is also a world where custom icons can be uploaded in the future and I wouldn't want to introduce another third column for that so I think it makes sense to keep it centralized.

In the medium term can probably rename the column on document from emoji -> icon to match and use the same schema.

[tommoor]

@hmacr still interested in taking this or shall we pass it along?

[hmacr]

@tommoor Oh yes definitely! I have been out for 2 weeks on personal time off.

I'm starting on #6215, and would take this one after that; so, in a day or two hopefully.
If customers are waiting for this feature, I can take it first; or pass it along too :)

[tommoor]

Upto you, all contributions appreciated equally