Don't try to correct `OT` in `OTK`

[dkasak]

OTK is a common term in cryptography, standing for One-Time Key. I couldn't quite figure out how to contribute the fix for this, but the following works locally:

[default.extend-identifiers]
OTK = "OTK"
OTKs = "OTKs"

[default.extend-words]
OTK = "OTK"
OTKs = "OTKs"

[epage]

For OTKs, see #745.

For OTK, its hard to tell when we should support terms specific to a subfield vs having users deal with it in their config. So far, I think we've tended to focus on more cross-domain terms or widely scoped domains.