Generate bom using java-platform plugin

[sghill]

What was changed

Added a temporal-bom subproject that publishes a bom using Gradle's java-platform plugin.

Most of the script plugins (dependencyManagement.gradle, java.gradle, etc) are built around the assumption each module is a java module. I excluded this project by name for this change.

Why?

BOMs are useful for keeping versions aligned, especially when they are brought in only as transitive dependencies.

Example without a bom:

runtimeClasspath
+--- org.example:some-library:1.0.0
|    +--- io.temporal:temporal-serviceclient:1.15 (misaligned)
\--- io.temporal:temporal-sdk:1.20

Other examples of java libraries producing similar boms: junit-bom, okhttp-bom

Checklist

How was this tested:

I ran ./gradlew :temporal-bom:generatePomFileForMavenJavaPublication and viewed the generated pom was expected.

Any docs updates needed?

Possibly an example of usage:

dependencies {
    implementation platform('io.temporal:temporal-bom:1.21.0-SNAPSHOT')
    implementation 'io.temporal:temporal-sdk' // no version necessary
    implementation 'io.temporal:temporal-remote-data-encoder'
    testImplementation 'io.temporal:temporal-testing'
}

[CLAassistant]

All committers have signed the CLA.

[cretz]

@Quinn-With-Two-Ns and @mjameswh - this was suggested via internal Slack thread and seems reasonable. May be worth a little due diligence to make sure it looks right and will publish properly.

[Quinn-With-Two-Ns]

LGTM CI is failing because you branch is missing tags

[sghill]

Thanks for the review @Quinn-With-Two-Ns! I rebased, pushed the tags to my branch, and it's green now.