migrate $ims config to new ims config

[shazron]

New config:

{
  "ims": {
    "config": {
      "plugins": [ "p1", "p2" ],
      "current": "sample"
    },
    "contexts": {
      "sample": {},
      "another": {}
    }
  }
}

Occurrences:

README.md:98:  Configuration for the Adobe IMS commands is stored in the "$ims"
README.md:117:       $ims: {
README.md:161:        e.g. aio config:set \$ims.your_context.your_context_key "your_context_value"
src/commands/auth/ctx.js:45:     e.g. aio config:set \\$ims.your_context.your_context_key "your_context_value"
src/commands/auth/index.js:32:Configuration for the Adobe IMS commands is stored in the "$ims"
src/commands/auth/index.js:52:    $ims: {
src/commands/auth/login.js:25:      // default is the `$cli` context, if $ims.$current not set
test/commands/auth/ctx.test.js:43:    $ims: {
test/commands/auth/ctx.test.js:52:  const IMS = '$ims.'
test/commands/auth/ctx.test.js:55:      return store.$ims[key.substring(IMS.length)]
test/commands/auth/ctx.test.js:62:      store.$ims[key.substring(IMS.length)] = value
test/commands/auth/ctx.test.js:72:  await expect(spy).toHaveBeenCalledWith(store.$ims.$current)
test/commands/auth/ctx.test.js:78:    data: store.$ims[myContext],
test/commands/auth/login.test.js:115:  const IMS = '$ims'
test/commands/auth/login.test.js:122:    store.$ims.$current = data
test/commands/auth/login.test.js:126:    return store.$ims.$current
test/commands/auth/logout.test.js:83:  const IMS = '$ims'
test/commands/auth/logout.test.js:90:    store.$ims.$current = data
test/commands/auth/logout.test.js:94:    return store.$ims.$current

Use a hook to auto-migrate, see adobe/aio-cli-plugin-console@ea1d6f4
Migrate $cli to cli as well.

Depends on adobe/aio-lib-ims#46