The type key should be required under aaa_server_groups and need to add defined check for servers key

[Shivani-gslab]

Issue Summary

• The type key under aaa_server_groups should be required as per EOS CLI.
• The servers key is not a required key but it has not been checked "if defined or not in the template", so it throws error if not defined. The template needs to be fixed.

aaa_server_groups:
    - name: TACACS
       type: tacacs+            ----------> [ this should be a required key ]
       servers:                     ----------> [ defined check should be added for this ] 
           - server: 10.10.11.157 
              vrf: mgt

Originally posted in PR #4626

         The `type` key should be `required` in schema.

Also, the same issue as tacacs server - servers key is not required but its not checked for defined in template so it throws error if not defined. (need to update j2 template)

Originally posted by @Shivani-gslab in #4626 (comment)

Steps to reproduce:

Give the following input to eos_cli_config_gen role -

aaa_server_groups:
    - name: TACACS
      type: tacacs+
    - name: TACACS2

[ClausHolbechArista]

In eos_cli_config_gen we try to just ignore incomplete entries. So just add if-defined checks in the templates. nevermind. when absolutely required for CLI I am ok with using the required in schema.