Adding *primer.bed file for midnight primer scheme

[henningonsbring]

The purpose of the code changes are as follows:

To enable analysis with the midnight primer scheme I am adding nCoV-2019.primer.bed in the midnight folder.

nCoV-2019.primer.bed is needed because of line 12 in artic.nf: path "${params.schemeDir}/${params.scheme}/${params.schemeVersion}/*.primer.bed" , emit: bed

Standard test procedure

• [ ] The self-test mentioned in the README finished successfully
• [ ] Produced files contain expected values
• [ ] The code has been reviewed by @octocat

This version is a:

• [ ] MAJOR - when you make incompatible API changes
• [x] MINOR - when you add functionality in a backwards compatible manner
• [ ] PATCH - when you make backwards compatible bug fixes or documentation/instructions