feat: Add Dev Server Integration

[cspath1]

In using the VSCode Extension during my day-to-day, one of the pain points I have with the extension is how it goes about handling toggling flags. Toggling a flag via the VSCode Extension (as it exists right now) will update the value in LaunchDarkly, meaning that users who have a shared environment with other developers will affect one another when toggling flags for testing.

Inspired in no small part to how the Developer Toolbar allows for a local means of overriding flag values without affecting other developers, I wanted to research and implement something similar, especially for developers working in more of a full-stack or back-end capacity. This PR introduces a tie-in to the ldcli dev-server allowing users to have an interface within their IDE to see dev-server flag values and locally override dev-server flag values. This functionality is not meant to replace any existing functionality, but enhance/take precedence when enabled.

It features:

• A command to connect to the ldcli dev-server. This command will default to using http://localhost:8765, but users can override this and the overridden value will be remembered for re-connecting in the future
• A command to set an override for a flag. This command will attempt to pull and showcase variation options, allowing for easy selecting of variations for string/number/json flags. If users wish to enter a custom value not covered by a defined variation, they can do so as well
• A command to remove an override for a flag (reset it to default dev-server value)
• The Feature Flags panel will easily show when a flag is overridden. Hovering over the flag (either via hovering over the flag key in your code or hovering over it in the Feature Flags panel) will show all of the existing information as well as the current dev-server value
• Code Lens (if enabled) will show the dev-server value + indicate whether or not the value is an overridden value
• If the value in the dev-server changes (i.e. by using the UI or another tool such as the Developer Toolbar), the extension listens and captures that change, keeping it up-to-date

Future Considerations:

• The overall login/auth flow remains the same for the VSCode Extension, however, I think that this feature set (especially if expanded) can pave the way for an Offline mode that has much of the same core functionality, but does not require generating/setting an access token
• We can look into adding ways to sync the dev-server from it's upstream source
• We can look into adding extension-based Context management (changing the Context of the dev-server, which would change default flag evaluations)

To-Do List before merging (given we like this):

• Update docs to highlight changes. We should also include a user guide for first time ldcli setup (for those using the VSCode Extension that want this functionality, but do not have the dev-server set up)
• Increment extension version. Is this a major version change?
• Is this something we want to release as a beta version? If so, let's do that and dogfood it first