Missing vCore parameter details in README and error message for `azure_manage_postgresql` role.

While writing the integration test, I got such failure:

TASK [cloud.azure_ops.azure_manage_postgresql : Create/Update PostgreSQL Server] ***
fatal: [testhost]: FAILED! => {"changed": false, "msg": "Error creating the PostgreSQL Server instance: (InvalidVcore) vCore value 2 is not valid. Please specify a valid vCore value.\nCode: InvalidVcore\nMessage: vCore value 2 is not valid. Please specify a valid vCore value."}

Although the README and the module do not mention the vCore parameter, from my understanding, it is related to the `azure_manage_postgresql_postgresql_sku`'s `capacity` variable. Therefore, I believe the first step should be to update the README file accordingly (including the name and valid range). Additionally, we need to specify the valid range for this parameter in the error message itself.

Further investigation is needed.