[Feature]: standard plugin prefix

Describe the proposed feature

Looks like most (all?) the plugins get names like "ocrmypdf_something". Would be great if ocrmypdf could try applying the standard prefix ocrmypdf_. This would save some typing (and retyping due to typing mistakes... the more you type the more you mistype). For instance, one could just say --plugin rapidocr and have it resolved as ocrmypdf_rapidocr automatically.