Add ui-model module info for media and audio (#2454)

This commit adds release info for two new modules: `media-ui-model` and `audio-ui-model`.

These modules provide data models for UI elements related to media and audio playback and settings.

They include README files with instructions on how to download and use the modules, and gradle properties for artifact information.

media/audio-ui-model/README.md

@@ -0,0 +1,21 @@
+# Audio Settings UI Model library
+
+[![Maven Central](https://img.shields.io/maven-central/v/com.google.android.horologist/horologist-audio-ui-model)](https://search.maven.org/search?q=g:com.google.android.horologist)
+
+For more information, visit the documentation: https://google.github.io/horologist/audio-ui-model
+
+## Download
+
+```groovy
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation "com.google.android.horologist:horologist-audio-ui-model:<version>"
+}
+```
+
+Snapshots of the development version are available in [Sonatype's `snapshots` repository][snap]. These are updated on every commit.
+
+  [snap]: https://oss.sonatype.org/content/repositories/snapshots/com/google/android/horologist/horologist-audio-ui-model/

media/audio-ui-model/gradle.properties

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+POM_ARTIFACT_ID=horologist-audio-ui-model
+POM_NAME=Horologist Audio Settings UI Model library
+POM_PACKAGING=aar

media/ui-model/README.md

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+# Media UI Model library
+
+[![Maven Central](https://img.shields.io/maven-central/v/com.google.android.horologist/horologist-media-ui-model)](https://search.maven.org/search?q=g:com.google.android.horologist)
+
+For more information, visit the documentation: https://google.github.io/horologist/media-ui-model
+
+## Download
+
+```groovy
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation "com.google.android.horologist:horologist-media-ui-model:<version>"
+}
+```
+
+Snapshots of the development version are available in [Sonatype's `snapshots` repository][snap]. These are updated on every commit.
+
+```groovy
+repositories {
+    maven { url "https://oss.sonatype.org/content/repositories/snapshots" }
+}
+
+dependencies {
+    implementation "com.google.android.horologist:horologist-media-ui-model:<version>-SNAPSHOT"
+}
+```
+
+[snap]: https://oss.sonatype.org/content/repositories/snapshots/com/google/android/horologist/horologist-media-ui/

media/ui-model/gradle.properties

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+POM_ARTIFACT_ID=horologist-media-ui-model
+POM_NAME=Horologist Media UI Model library
+POM_PACKAGING=aar