[SVCS-528] Improve gdoc rendering - MFR Part

[cslzchen]

Ticket

https://openscience.atlassian.net/browse/SVCS-528 WB counterpart: https://github.com/CenterForOpenScience/waterbutler/pull/304

Purpose

This PR replaces https://github.com/CenterForOpenScience/modular-file-renderer/pull/292. Credit goes to @AddisonSchiller 🎆 🎆 .

• Let WB know that the request is from MFR.
• When rendering .gdoc, MFR will receive a .pdf from WB and render this file using pdf renderer.

Changes

• Append a mfr query param to WB urls to let it know the request is coming from MFR.
• Move .gdoc extension from unoconv renderer/exporter to pdf renderer

Side effects

None

QA Notes

Test that .gdoc rendering works as usual.

Deployment Notes

This PR must be merged/deployed at the same time as its WB counterpart. Same to the WB PR, this is blocked by @TomBaxter 's V3 update: https://github.com/CenterForOpenScience/waterbutler/pull/276.

[coveralls]

Coverage increased (+0.02%) to 68.034% when pulling 9d9ccec5fab170d976d20a9bfb94690e06f355a6 on cslzchen:feature/svcs-528-improve-gdoc into 8bb2dd4d35f8c1d89a72fc8b9e09db317f3497f3 on CenterForOpenScience:develop.

[coveralls]

Coverage remained the same at 68.016% when pulling 5a88dd52e596a62b8f6c2535ec5b09b0d8b99175 on cslzchen:feature/svcs-528-improve-gdoc into 8bb2dd4d35f8c1d89a72fc8b9e09db317f3497f3 on CenterForOpenScience:develop.