enhance action create with env variables

**Describe the bug**
This was missed in the recently merged PR #103. The `-P` flag is overloaded to mean read params from file and read env from file. This is a copy/paste bug, the intent was to use `-E`.

https://github.com/adobe/aio-cli-plugin-runtime/pull/103/files#diff-6d51d7a8679a906a9bfdaf1a8b017006R207

Thanks to @purplecabbage for pointing this out. We were both surprised oclif didn't barf at this.

As an enhancement, Jesse also suggested supporting reading the value of an env var from the shell environemnt, so that you can do `... action create myAction -e FOO` which is syntactic sugar for `... action create myAction -e FOO $FOO`. I think this is neat/convenient (perhaps to be considered separately as an enhancement).

检查 PR #103 中链接位置的 action create 选项处理，重点关注具有重载含义的 -P 标志和预期的 -E 标志。确认现有的参数文件行为，然后确定是否包含 shell 环境查找，还是将其单独处理；完成意味着这些标志具有不同的行为，并且所请求的命令用法已由测试覆盖。

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