Yaml bases resolve / completion for 'config and pep.config`

[iromeo]

Yaml keys completion for config and pep.config objects (e.g. see #360 issue)

Expected completion:

• in python code: config['<..>'], config['key1']["<..>"]

• in SnakemakeSL: `shell: "echo config[key1][key2]"

• Completion both for config[] and pep.config[]

• pepfile and configfile declarations could be missing, e.g. user attach them only on runtime. In this case we need a way how to configure which keys are available for completion. So 2 options:

  • take keys from pepschema (not clear what to do with config) or
  • provide UI in project settings (e.g. in snakemake framework support page) which allows to configure available keys (leaf and intermediate nodes)

• Subtask: config support, see Resolve/completion for config attrs #5