Add @WorkflowInit docs for Java

[Quinn-With-Two-Ns]

What does this PR do?

Add @WorkflowInit docs for Java based on the Python docs for the same feature https://github.com/temporalio/documentation/pull/3108

Notes to reviewers

Note sure if we need to callout the SDK version this feature is available in? We didn't in Python, but maybe we should have?

[fairlydurable]

Removed parentheses. Uppercased Workflow. Will align with .NET in future ticket.

[fairlydurable]

Parenthesis returned to link.

[fairlydurable]

Thank you for putting this together @Quinn-With-Two-Ns and @drewhoskins-temporal