aws: set AWS_EB_PROFILE for the EB CLI (#7388)

Added AWS_EB_PROFILE environment variable to the AWS Plugin. The EB CLI uses this
variable instead of the primary AWS_PROFILE variable to keep track of what profile
it is using.

https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/eb-cli3-configuration.html

plugins/aws/README.md

@@ -12,6 +12,7 @@ plugins=(... aws)
 ## Plugin commands
 
 * `asp [<profile>]`: Sets `$AWS_PROFILE` and `$AWS_DEFAULT_PROFILE` (legacy) to `<profile>`.
+  It also sets `$AWS_EB_PROFILE` to `<profile>` for the Elastic Beanstalk CLI.
   Run `asp` without arguments to clear the profile.
 
 * `agp`: Gets the current value of `$AWS_PROFILE`.

plugins/aws/aws.plugin.zsh

@@ -7,6 +7,7 @@ function agp {
 function asp {
   export AWS_DEFAULT_PROFILE=$1
   export AWS_PROFILE=$1
+  export AWS_EB_PROFILE=$1
 
   if [[ -z "$1" ]]; then
     echo AWS profile cleared.