Add a plugin entry point bundle size budget

[joshdover]

Related to #70733

The most significant cause of slow page load times in Kibana appears to be from plugin entry point bundles that grow in size over time. Usually, this happens by accident. An additional import for something small ends up pulling in large parts of a tree.

While there are many ways to address this, a simple way to get ahead of this problem is to prevent PRs from being merged if they dramatically increase the size of a entry point bundle(s). Now that we are tracking metrics of these plugin bundles in CI, we should introduce a "budget" that each plugin must comply with.

To start, our goal is to get every plugin bundle under 200kb, uncompressed. We have a few dozen that do not comply with this today, and for these we should have an exception list while we work on reducing these problematic bundles.

Once all bundles are under the 200kb limit, we can start ratcheting down this limit over time. When a PR increases a bundle's size over the specified budget, CI should fail.

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)