Add support for config file for running e2e tests

[chatton]

Problem Definition

Our current e2e tests rely solely on environment. variables for configuration. This is fine when there are relatively few variables, but as our tests have gotten more involved, there have been more and more configuration options being added.

Proposal

Add file that enables granular configuration over test settings.

Here is an example for what this might look like

{
   "chains":[
      {
         "chainId":"chain-a",
         "numValidators":4,
         "numFullNodes":1,
         "image":"ghcr.io/cosmos/ibc-go-simd",
         "tag":"main",
         "binary":"simd"
      },
      {
         "chainId":"chain-b",
         "numValidators":4,
         "numFullNodes":1,
         "image":"ghcr.io/cosmos/ibc-go-simd",
         "tag":"main",
         "binary":"simd"
      }
   ],
   "relayer":{
      "type":"rly",
      "image":"ghcr.io/cosmos/relayer",
      "tag":"main"
   },

   "upgrade": {
       "planName": "normal upgrade",
       "tag": "v7.0.0-rc0"
    }
}

We can allow the environment variables to take precedence so we don't need to modify our CI immediately.

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