Parse platform.json, hwsku.json for generate minigraph

[dmytroxshevchuk]

Description of PR

After transition from port_config.ini to platform.json, hwsku.json, we can`t fully deprecate and remove port_config.ini cause of port_mgmt/ansible use port_config.ini for generate minigraph. So currently we have configuration(platform.json, hwsku.json) using by sonic for configure ports and configuration(port_config.ini) using by sonic_mgmt for generate minigraph. So changes in platform.json and hwsku.json will not affect minigraph because of port_config.ini so we have configuration mismatch.
PR add functionality to sonic_mgmt for parse platform.json and hwsku.json and use this configuration for generation minigraph.

Summary:
Fixes # (issue)

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• Test case(new/improvement)

Approach

What is the motivation for this PR?

• fully deprecate and remove port_config.ini
• avoid mismatch configurations between port_config.ini and platform.json, hwsku.json

How did you do it?

Add functionality for parsing platform.json, hwsku.json and use this configuration for generate minigraph.

How did you verify/test it?

Compare generated minigraph/config_db configurations with platform.json, hwsku.json.

Any platform specific information?

Supported testbed topology if it's a new test case?

Documentation

[SavchukRomanLv]

@wangxin @yxieca could you please take a look? Thank you in advance!

[yxieca]

@jleveque @theasianpianist , the change looks good to me. Can you guys also take a look?

[theasianpianist]

Please use the testmg.sh script to verify your changes.

[yxieca]

@dmytroxshevchuk I need to revert this PR. We found following issue with platform.json as grant truth:

For example, on a Mellanox 2700 device, if we want to deploy the 100G topology:

The platform.json's alias table:
"alias_at_lanes": "etp1a, etp1b, etp1c, etp1d",

ept1a would be used for Ethernet0's alias and that causes minigraph generation error.

With non-breakout topologies, the alias should be etp1.

[dmytroxshevchuk]

@yxieca issue with platform.json was fixed in sonic-buildimage
issue for that: sonic-net/sonic-buildimage#6024
PR for that: sonic-net/sonic-buildimage#6831
So I created another PR with the same changes considering on Mellanox platform.json issue.
Please take a look:
#3469