Make rc release possible

[MiloszFilimowski]

Description

• Add --tag rc to npm publish in the release workflow when the GitHub release is marked as a pre-release
• Uses github.event.release.prerelease to conditionally append the tag across all four publish jobs (webrtc-client, ts-client, react-client, mobile-client)

Motivation and Context

Publishing a prerelease version (e.g. v0.26.0-rc.0) without --tag fails on npm 10+ because npm refuses to publish prereleases to the latest dist-tag by default.

Documentation impact

• Documentation update required
• Documentation updated in another PR
• No documentation update required

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)