Add the PS FORMAT VCF standard header field

[nh13]

@lbergelson
Motivated by broadinstitute/gatk#5318

I am happy to change the language as folks see fit.

[codecov-io]

Codecov Report

Merging #1200 into master will increase coverage by 0.013%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##              master     #1200       +/-   ##
===============================================
+ Coverage     68.503%   68.516%   +0.013%     
- Complexity      8032      8034        +2     
===============================================
  Files            542       542               
  Lines          32714     32715        +1     
  Branches        5534      5534               
===============================================
+ Hits           22410     22415        +5     
+ Misses          8099      8097        -2     
+ Partials        2205      2203        -2

Impacted Files	Coverage Δ	Complexity Δ
...ava/htsjdk/variant/vcf/VCFStandardHeaderLines.java	76.389% <100%> (+0.333%)	11 <0> (ø)	⬇️
...va/htsjdk/samtools/sra/SRAIndexedSequenceFile.java	64.865% <0%> (+2.703%)	7% <0%> (+1%)	⬆️
...samtools/util/AsyncBlockCompressedInputStream.java	76% <0%> (+4%)	13% <0%> (+1%)	⬆️

[lbergelson]

@nh13 Thank you. This seems good to me.

[lbergelson]

Lets give it another day or two to let people have a chance to see it in case there are any suggestions to the phrasing.

[lbergelson]

No one responded so I'm going to merge this. Thank you @nh13