Jobs section for profile.wordpress.org: move current job info into new section

[annezazu]

Right now, we don't have a way to show you are currently working a job on your profile. Here's what LinkedIn does:

[annezazu]

Ah, just realized we ask for this in the first section of the profile: https://profiles.wordpress.org/profile/edit/group/1/

We need to better connect these 🤔 . Let's move the above into the new Jobs section. It's where users would expect to find it and it's better to have it all centralized. Renaming this issue. Here's a very simple design reusing what's already there and just removing the end date:

[bor0]

Addressed this in r24630

[bor0]

@annezazu had additional comment about the date component, which I updated in r24631