feat: rename --dotenv to --env-file

Add --env-file as an alias for the existing --dotenv flag.

"--dotenv" is a confusing name when saying it out loud (e.g. on
a support call). "--env-file" is more precise and is also used
by Node.js v20 and above:

https://nodejs.org/dist/latest-v20.x/docs/api/cli.html#--env-fileconfig

packages/artillery/lib/cli/common-flags.js

@@ -23,7 +23,8 @@ const CommonRunFlags = {
     description: 'Write a JSON report to file'
   }),
   dotenv: Flags.string({
-    description: 'Path to a dotenv file to load environment variables from'
+    description: 'Path to a dotenv file to load environment variables from',
+    aliases: ['env-file']
   }),
   variables: Flags.string({
     char: 'v',