Feat: command for installing specific Python runtime

## Describe Request:

I am hoping if it is possible to extend this Orb to include a `install` command, [much like the Node Orb's](https://github.com/CircleCI-Public/node-orb/blob/master/src/commands/install.yml).

In our use case, we have a job running on a non-Python executor (e.g., Ruby related). Since multiple executors for supporting multiple language runtime environments are not feasible, I end up having to specifically install a Python runtime in a job's step. If there was something like what the Node Orb's `install` command offers, this would have been great (one-liner or so for me!)

## Examples:

```diff
# job
my_custom_job:
docker:
- image: circleci/ruby:2.7.2
steps:
- checkout
+ - python/install:
+ python-version: '3.8.7'
- run:
command: |
which python3.8
```

Start by comparing the referenced Node Orb command at src/commands/install.yml with the existing python-orb commands and configuration. Verify the proposed python/install step accepts the shown Python version on a non-Python executor and makes the requested interpreter available to subsequent steps.

索引モデルが issue の本文から書いたものです。