Knob to enable bandwidth plugin

[jayanthvn]

What type of PR is this?
Feature

Which issue does this PR fix:
Update 10-aws.conflist file when bandwidth plugin is needed

What does this PR do / Why do we need it:
When knob is enabled , we add bandwidth plugin to 10-aws.conflist file.

Also fixes #1437

If an issue # is not available please add repro steps and logs from IPAMD/CNI showing the issue:
n/a

Testing done on this change:

[root@ip-192-168-32-207 ec2-user]# cat /etc/cni//net.d/10-aws.conflist 
{
  "cniVersion": "0.3.1",
  "name": "aws-cni",
  "plugins": [
    {
      "name": "aws-cni",
      "type": "aws-cni",
      "vethPrefix": "eni",
      "mtu": "1500",
      "pluginLogFile": "/var/log/aws-routed-eni/plugin.log",
      "pluginLogLevel": "Debug"
    },
    {
      "type": "portmap",
      "capabilities": {
        "portMappings": true
      },
      "snat": true
    },
    {
      "type": "bandwidth",
      "capabilities": {
        "bandwidth": true
      }
    }
  ]
}

Disable ENABLE_BANDWIDTH_PLUGIN

[root@ip-192-168-32-207 ec2-user]# cat /etc/cni//net.d/10-aws.conflist 
{
  "cniVersion": "0.3.1",
  "name": "aws-cni",
  "plugins": [
    {
      "name": "aws-cni",
      "type": "aws-cni",
      "vethPrefix": "eni",
      "mtu": "1500",
      "pluginLogFile": "/var/log/aws-routed-eni/plugin.log",
      "pluginLogLevel": "Debug"
    },
    {
      "type": "portmap",
      "capabilities": {"portMappings": true},
      "snat": true
    }
  ]
}

Automation added to e2e:

Will this break upgrades or downgrades. Has updating a running cluster been tested?:
No

Does this change require updates to the CNI daemonset config files to work?:

Yes, if user needs bandwidth plugin

Does this PR introduce any user-facing change?:

Bandwidth plugin support

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[M00nF1sh]

looks good to me, except would like to understand why we don't enable it by default like the portmap.
e.g. will it introduce performance issues if ppl don't use the bandwidth functionality?

[M00nF1sh]

/lgtm