Process config files for profile names containing prefix separator

[trivikr]

Issue #, if available:

• Fixes: Recent change causes profile names with '.' to not be recognized or found #1053
• Fixes: Profile not found on profile names containing a "." aws/aws-sdk-js-v3#5521

Description of changes:

Validate IniSectionType for profile names containing config prefix separator

Testing:

$ cat test.mjs
import { loadSharedConfigFiles } from "../smithy-typescript/packages/shared-ini-file-loader/dist-cjs/index.js";
console.log(await loadSharedConfigFiles());

$ cat ~/.aws/credentials
[foo.bar]
aws_access_key_id = aws_access_key_id
aws_secret_access_key = aws_secret_access_key

[foo@bar]
aws_access_key_id = aws_access_key_id
aws_secret_access_key = aws_secret_access_key

$ cat ~/.aws/config
[profile foo.bar]
region = eu-west-2

[profile foo@bar]
region = eu-west-2

$ node test.mjs
{
  configFile: {
    'foo.bar': { region: 'eu-west-2' },
    'foo@bar': { region: 'eu-west-2' }
  },
  credentialsFile: {
    'foo.bar': {
      aws_access_key_id: 'aws_access_key_id',
      aws_secret_access_key: 'aws_secret_access_key'
    },
    'foo@bar': {
      aws_access_key_id: 'aws_access_key_id',
      aws_secret_access_key: 'aws_secret_access_key'
    }
  }
}

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