Add preparing and finalizing text to upload progress.

[leilenah]

Reasons for making this change

It can be confusing to a user if upload UI hangs at 0% or 100%. This is not really an issue with small files, but can happen if the user is trying to upload a large file.

This change adds a preparing and finalizing indicator to the upload progress UI.

Related issues

#4137
#4177

Screenshots

Before (prod)

20220907203742231.mp4

After (local)

20220907203847280.mp4

Checklist

• I've added a screenshot of the changes, if this is a frontend change
• I've added and/or updated tests, if this is a backend change
• I've run the pre-commit.sh script
• I've updated docs, if needed

[percyliang]

Nice touch. Later, we might want to provide users with more insight into what's going on in the preparing and finalizing stages..