Update "Create a new branch from an issue" section to reflect latest UI.

Update Web Editor docs to reflect latest Create Branch UI

The "Create Branch" button no longer exists, it is now a dropdown. This updates the documentation to more closely match the current UI.

Does this MR meet the acceptance criteria?

Conformity

(please advise if anything else is needed for this doc-only fix MR)

• Changelog entry (not required for doc-only changes)
• Documentation (if required)
• Style guides

Availability and Testing

Doc-only changes, not applicable

Security

Doc-only changes, not applicable