Allow users to specify settings of Copilot LSP

[jmpunkt]

Feature

This allows users to set the settings (https://github.com/github/copilot-language-server-release?tab=readme-ov-file#configuration-management) for the Copilot LSP. VSCode stores this in settings.json? Having this feature allows users to login into GitHub Enterprise instances. Without this it is not possible. You can also disable telemetry with this.

How To Test

Testing this without a GHE instance is tricky but doable.

1. Start Emacs and evaluate this PR.
2. Log out of your current session (M-x copilot-logout).
3. Use eval-last-sexp (C-x C-e) to step through the following snippets

(copilot--start-agent)
(copilot-login)
;; you should be able to login, everything works fine (abort login C-g)
(setopt
 copilot-lsp-settings
 '(:github-enterprise (:uri "https://example2.ghe.com")))
(copilot-login)
;; there should be an error, the instance does not exist, the error code shows the url

Another test can be:

(setq copilot-log-max 2000)
(copilot--start-agent)
(switch-to-buffer-other-window "*copilot events*")
(setopt
 copilot-lsp-settings
 '(:github-enterprise (:uri "https://example2.ghe.com")))
;; you will see in the log that the telemetry tries to fetch from the instance (with an error of course)
(setopt
 copilot-lsp-settings
 '(:github-enterprise (:uri "https://example2.ghe.com")
   :telemetry (:telemetryLevel "all")))
;; now the previous telemetry error is gone

[bbatsov]

I think you should also mention this in the README.

[jmpunkt]

I added the README entry. If there is something else missing, then let me know.

[bbatsov]

I think "copilot--notify-configuration-changed" is probably a better name for this function.

[jmpunkt]

This function got removed. We only notify the server at the start now.

[bbatsov]

Add a :package-version property mentioning this got added in version 0.2.

[bbatsov]

I'm reasonably certain this will be triggered only when using M-x customize, so you'll probably have to mention it somewhere, so people are not surprised that manual config changes don't trigger it.

[bbatsov]

You should probably add a note that's supposed to get triggered when copilot-lsp-settings gets updated via the customize UI. Such callbacks are rarely used and might surprise many users.

[bbatsov]

I've added a few small remarks here and there, but overall your changes are in a good shape.

[jmpunkt]

Thanks for the review. I had to change one thing. There is an issue with the notify when changing the settings from something (e.g. '(:github-enterprise (:uri "test.com"))) to nil. The change is not recognized by the LSP. We would have to send '(:github-enterprise (:uri nil)) instead, in order to apply the change. So I restart the agent every time the settings change. Otherwise, we would have to calculate the difference between the old and new value.

[bbatsov]

Great work! Thanks!