add task for pangolin v4

[kapsakcj]

v4 hasn't been released just yet, but would be good to have a task ready to go when the time comes

will require:

• a new WDL task
• updates to all WDL workflows that call the pangolin4 task
• new docker image, with the cache of precomputed assignments included
• using the new default mode of pangolin (UShER). no more --usher flag required

docs on usage here: https://cov-lineages.org/resources/pangolin/usage.html Looks to be similar to v3

docs on output format here: https://cov-lineages.org/resources/pangolin/output.html

[kapsakcj]

working on this dev branch https://github.com/theiagen/public_health_viral_genomics/tree/cjk-pangolin-v4-dev

added task pangolin4, but need to update all workflows that call the task.

task_taxonID.wdl passes miniwdl check but needs to be tested with real data