fix asciiidoc attributes for the migration procedure

There is something strange here [1].
It must be accordingly to the PR [2]:
export PRE_MIGRATION_PRODUCT_SHORT_ID=codeready
export PRE_MIGRATION_PRODUCT_DEPLOYMENT_NAME=codeready
export PRE_MIGRATION_PRODUCT_OPERATOR_NAME=codeready-operator
export PRE_MIGRATION_PRODUCT_CHE_CLUSTER_CR_NAME=codeready-workspaces
export PRE_MIGRATION_PRODUCT_SUBSCRIPTION_NAME=codeready-workspaces
but I found:
export PRE_MIGRATION_PRODUCT_SHORT_ID=devspaces
export PRE_MIGRATION_PRODUCT_DEPLOYMENT_NAME=devspaces
export PRE_MIGRATION_PRODUCT_OPERATOR_NAME=devspaces-operator
export PRE_MIGRATION_PRODUCT_CHE_CLUSTER_CR_NAME=devspaces
export PRE_MIGRATION_PRODUCT_SUBSCRIPTION_NAME=devspaces
[1] https://red-hat-developers-documentation.pages.redhat.com/red-hat-devtools/devspaces/asciidoctor/administration-guide/#upgrading-dev[...]-on-openshift
[2] https://github.com/eclipse-che/che-docs/pull/2308