Linkage Monitor GitHub Action to take input of BOM coordinates

[suztomo]

Linkage Monitor for java-spanner version 4.0.0 branch is not working. The check is designed to always to choose the latest version in the Libraries BOM.

@BenWhitehead 's idea: add new parameter to linkage monitor to provide the bom to validate against [groupId:artifactId[:version]]

• if not specified version would default to latest
• if groupId:artifactId are not specified it would default to com.google.cloud:libraries-bom

[BenWhitehead]

Thanks for creating the feature request @suztomo!