rel: [network-agent] prepare first alpha release

[JamieDanielson]

Which problem is this PR solving?

Lack of a published helm chart for the Honeycomb Network Agent.

• Closes https://github.com/honeycombio/honeycomb-network-agent/issues/235

Short description of the changes

• Add changelog
• (no changes to version because this is the first one and it's already set to 0.0.1-alpha)