Mark transitive dependencies optional

[cowwoc]

Describe the bug
client-java depends on io.prometheus:* and com.com.amazonaws:*. Both dependencies pull in needless transitive dependencies for users who don't use prometheus or aws.

Client Version
21.0.1

Expected behavior
Review all dependencies as mark as many as possible as optional. See https://maven.apache.org/guides/introduction/introduction-to-optional-and-excludes-dependencies.html for more information.

[brendandburns]

Happy to take PRs to improve/add the right optional dependencies for libraries related to auth.

Removing prometheus may be trickier, but again, open to reviewing PRs

Thanks