Cody Ignore: Add an action to override the Cody Ignore policy for testing

[dominiccooney]

This adds some plumbing for Cody Ignore, and a way to interactively test that locally in IntelliJ without admin access to a Sourcegraph instance.

• Adds Agent protocol stubs for Cody Ignore protocol. These depend on Agent-side changes in Elaborate the agent protocol for Cody Ignore cody#3858
• Adds an "internals" menu to the status bar, hidden behind a feature flag, for doing ad-hoc manual ignore policy settings

Part of #1252

Test plan

• Run agent with Elaborate the agent protocol for Cody Ignore cody#3858
• Run the plugin with CODY_JETBRAINS_FEATURES=cody.feature.internals-menu=true and open a clone of the sourcegraph/sourcegraph repo
• On the status bar, Internals, Testing: Cody Ignore
• Check Override policy for testing
• Enter URI regex \.go$ . Any repo regex is fine; that setting is currently unused on the extension side. Click OK.
• Verify that console output includes handling ignore rules changing not yet implemented. This indicates the testing override generated a notification that the rules have changed, through to the stub in the extension.
• Start a chat
• In the Enhanced Context Selector, ensure Chat Context is checked. Uncheck any specific repos.
• Open a Go file, for example cmd/batcheshelper/main.go and highlight some code
• In chat, ask Cody "what does this do?" There should be no local context and Cody should make something up unrelated to the highlighted code.
• On the status bar, Internals, Testing: Cody Ignore. Uncheck Override policy for testing. OK. Again verify console output.
• In chat, hit up and resubmit the same chat message. There should be local context from the open Go file and Cody should comment related to that code.
• Run the plugin again without CODY_JETBRAINS_FEATURES=cody.feature.internals-menu=true and verify that the Internals menu does not appear on the status bar.

[pkukielka]

LGTM

[odisseus]

Why not enum?

[dominiccooney]

We tend to just enumerate the string values, but I will look into it in a follow-up. There's no JetBrains side calls to this yet.