[Fern's Documentation] Update "Publish a Java SDK to Maven Central" Registration Process

[amy-keibler]

What can be improved

Hello, I'm opening this on behalf of the Maven Central team. We just wanted to let you know that our Account Registration and Namespace / groupId Registration processes have changed, so the fern/docs/pages/fern-sdks/guides/publish-to-maven-central.mdx documentation is no longer accurate. We got a support request by a user that mentioned that documentation, so we thought it would be a good idea to reach out.

(if you're curious about the details, we deprecated issues.sonatype.org due JIRA on-prem reaching its end-of-life)

Relevant Screenshots

The content to be reworked would be steps 2-5, but we can provide screenshots if that is desired.

Link a PR (optional)

[dannysheridan]

Hey @amy-keibler thanks for letting us know! This is really helpful.

Would you be up to make a contribution? Here's the Markdown behind that page: https://github.com/fern-api/fern/blob/main/fern/docs/pages/fern-sdks/guides/publish-to-maven-central.mdx