Updated documentation to show custom S3 component configuration in registry

[spaul-ngp]

• Make sure there is a JIRA issue filed for the change (usually before you start working on it). Trivial changes like typos do not require a JIRA issue. Your pull request should address just this issue, without pulling in other changes.
• Each commit in the pull request should have a meaningful subject line and body.
• If you're unsure, you can format the pull request title like [CAMEL-XXX] Fixes bug in camel-file component, where you replace CAMEL-XXX with the appropriate JIRA issue.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Run mvn clean install -Psourcecheck in your module with source check enabled to make sure basic checks pass and there are no checkstyle violations. A more thorough check will be performed on your pull request automatically.
  Below are the contribution guidelines:
  https://github.com/apache/camel/blob/master/CONTRIBUTING.md

[oscerd]

Thanks