Process sso-session names with config prefix separator

[trivikr]

Issue #, if available:
Fixes: #1163

Description of changes:
Process sso-session names with config prefix separator

Testing:

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

$ cat ~/.aws/config
[profile my.big.profile]
region = us-east-1
sso_session = my.sso
sso_account_id = 123456789
sso_role_name = BigRole

[sso-session my.sso]
sso_region = us-east-1
sso_start_url = https://magic-app.awsapps.com/start
sso_registration_scopes = sso:account:access

$ node test.mjs 
{
  'my.sso': {
    sso_region: 'us-east-1',
    sso_start_url: 'https://magic-app.awsapps.com/start',
    sso_registration_scopes: 'sso:account:access'
  }
}

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