Add args section in meta.yml

Description of feature

As discussed in the slack thread

In @jfy133 words:

We need a new section for listing each args (2, 3, 4) with the sole(?) metadata
for each one is simply the tool of the pipe it is effecting.

In @mirpedrol words:

We want an extra section in the meta.yml to describe the ext.args values.
At the level of tools , inputs and outputs.

It would look like this:

tools:
  - "bcftools":
      description: "..."
      homepage: ...
      args_id: "$args"
      identifier: biotools:bcftools
  - "bcftools plugin setGT":
      description: "..."
      homepage: ...
      args_id: "$args2"
      identifier: biotools:bcftools
args:
  - args:
      description: ""
  - args2:
      description: ""
input:
  - - meta:
        ...
    - vcf:
        ...

Start by reviewing the existing meta.yml structure, especially the tools, input, and output sections, then read the linked Slack discussion for the intended args metadata model. Done means the project has an agreed and implemented schema for describing ext.args values and their associated tools, inputs, and outputs.