feat(cli): Allow to override variable

[m-mizutani]

The PR allows to override environment variable by multiple -e option.

$ cat .env
POSTGRES_DB=your_local_db
POSTGRES_USER=test_user
$ cat .env.local
POSTGRES_DB=your_local_dev_db
$ zenv -e .env -e .env.local psql
# Access to your_local_dev_db with test_user

The priority for loading environment variables is as follows: first, the -e option, followed by additional -e options, and finally, the arguments of the zenv command.

$ cat .env1
COLOR=blue
$ cat .env2
COLOR=orange
$ zenv -e .env1 -e .env2 COLOR=red echo %COLOR
red

[octovy-dev]

🎉 No vulnerability detected 🎉