Prepare the release/3.0.0 branch to produce release GA builds. (#434)

This removes the pre.18 tag from everything but the accessibility and
data packages.

<img width="473" alt="image"
src="https://github.com/MixedRealityToolkit/MixedRealityToolkit-Unity/assets/9615036/6b3b03be-7595-451a-b1e8-57f3f4a29718">

Author: shaynie

Pipelines/Config/settings.yaml

@@ -6,4 +6,4 @@ variables:
   # ProjectSettings/ProjectSettings.asset:  metroPackageVersion: x.x.x.0
   MRTKVersion: 3.0.0        # used for overall build number, but each package version is read from the package.json file in each package directory.
   MRTKReleaseTag: 'pre.18'  # final version component, e.g. 'RC2.1' or empty string.
-  ReleasePackages: 'None'   # array of packages that shouldn't get the prerelease tag  e.g.  '"org.mixedrealitytoolkit.core,org.mixedrealitytoolkit.tools"'
+  ReleasePackages: 'org.mixedrealitytoolkit.audio,org.mixedrealitytoolkit.core,org.mixedrealitytoolkit.diagnostics,org.mixedrealitytoolkit.extendedassets,org.mixedrealitytoolkit.input,org.mixedrealitytoolkit.spatialmanipulation,org.mixedrealitytoolkit.standardassets,org.mixedrealitytoolkit.tools,org.mixedrealitytoolkit.uxcomponents,org.mixedrealitytoolkit.uxcomponents.noncanvas,org.mixedrealitytoolkit.uxcore,org.mixedrealitytoolkit.windowsspeech'   # array of packages that shouldn't get the prerelease tag  e.g.  '"org.mixedrealitytoolkit.core,org.mixedrealitytoolkit.tools"'