Look up "developer relations". It's kind of being an advocate for the software made by a company. Part of that job is to have respect so open source advocacy goes with it. Double goes with it if the software made by the company is open source.
I believe organizations like the FSF, FSFE and SF Conservancy employ basically lobbyists to help represent open-source.
And organizations like Mozilla, KDE, GNOME, openSUSE, The Document Foundation, Wikimedia etc. will have basically open-source community managers. So, where you could potentially help to steer an open-source community, as far as that's possible.
But yeah, these positions are extremely rare. Like, we're talking a few dozens on the whole planet.
People in these positions usually have made a name for themselves in other ways and have experience in similar jobs...
Yes. However, such positions are not common, because they rely on a pre-allocated pile of money being dedicated towards FLOSS.
When I was at Oregon State University, I worked for the Open Source Lab; you may recognize them as an option on your distro's mirror list. During part of that time, I worked for the Open Source Education Lab, an outreach program which was funded by a grant through the College of Electrical Engineering and Computer Science (now the College of Electrical & Computer Engineering). This grant funded some get-togethers on campus, the local Linux Users Group, and some one-off interactions like giving talks to undergraduate classes about how to use FLOSS software.
But, when the grant ended, so did OSEL. OSL and the LUG are still around because their funding comes from OSL tenants and LUG club members respectively, but they are not focused on outreach and advocacy.
I was actually a music major! Software engineering is my backup career, but back then, it was my dayjob; I wrote code for the university during the day, and played music at local clubs at night.
I don't think they will, there are thousands of people already doing it for free, you'll likely find one such person in any mid-size business wiring up your network cables.
You'll have much better chances to get paid if you provide some business model how to contribute to open-source software while keeping your profits flowing, because the business is all about competition and keeping things secret, and there are very few successful businesses based on open-sourcing their work.
It is, for example, EFF has paid positions, and they're huge advocates of FoSS. "Opensource Advocacy" is not the job/job-title, but it's part of the job
Also there are companies that are FoSS at it's core - but get paid by clients for consultancy work for support and implementation of their FoSS. They have paid positions for advocacy for their software