Populate sso-session and services sections when loading config files

[trivikr]

Issue #, if available:
Fixes: #991

Description of changes:
Populate sso-session and services sections when loading config files

• Adds enum IniSectionType in @smithy/types
• Populates sections in parseIni by using CONFIG_PREFIX_SEPARATOR between prefix and config name.
• Replaces redundant utility getProfileData with getConfigData

Tested with relative import from bug report in #991

Code:

// ...
import { loadSharedConfigFiles } from "../smithy-typescript/packages/shared-ini-file-loader/dist-cjs/index.js";
// ...

sso-session:

{
  "configFile": {
    "profile-with-sso-session": {
      "sso_session": "my-sso",
      "sso_account_id": "111122223333",
      "sso_role_name": "SampleRole"
    },
    "sso-session.my-sso": {
      "sso_region": "us-east-1",
      "sso_start_url": "https://my-sso-portal.awsapps.com/start"
    }
  },
  "credentialsFile": {}
}

services:

{
  "configFile": {
    "profile-with-services": {
      "services": "my-services",
      "endpoint_url": "http://localhost:5567"
    },
    "services.my-services": {
      "s3.endpoint_url": "https://localhost:1234"
    }
  },
  "credentialsFile": {}
}

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