chore(plg): add useEmbeddedUI site config param (#63442)

Adds `dotcom.codyProConfig.useEmbeddedUI` site config param. 
This param defines whether the Cody Pro subscription and team management
UI should be served from the connected instance running in the dotcom
mode. The default value is `false`. This change allows us to enable the
SSC proxy on the instance without enabling the new embedded Cody Pro UI.

Previously whether the embedded Cody Pro UI is enabled was defined by
the `dotcom.codyProConfig` being set, which prevented us from enabling
the SSC proxy without enabling the embedded UI:
> Whether the SSC proxy is enabled is [defined based on
`dotcom.codyProConfig`](https://github.com/sourcegraph/sourcegraph/blob/41fb56d619b82ee7f896a2e8aaf5937782731660/cmd/frontend/internal/ssc/ssc_proxy.go#L227-L231)
being set in the site config. This value is also partially
[propagated](https://github.com/sourcegraph/sourcegraph/blob/41fb56d619b82ee7f896a2e8aaf5937782731660/cmd/frontend/internal/app/jscontext/jscontext.go#L481)
to the frontend via jscontext. And the frontend [uses this
value](https://github.com/sourcegraph/sourcegraph/blob/41fb56d619b82ee7f896a2e8aaf5937782731660/client/web/src/cody/util.ts#L8-L18)
to define whether to use new embedded UI or not.

For more details see [this Slack
thread](https://sourcegraph.slack.com/archives/C05PC7AKFQV/p1719010292837099?thread_ts=1719000927.962429&cid=C05PC7AKFQV).

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## Test plan
- CI
- Tested manually:
  - Run Sourcegraoh instance locally in dotcom mode
  - Set `dotcom.codyProConfig` in the site config
- Type `context. frontendCodyProConfig` that it returns the [correct
values from the site
config](https://github.com/sourcegraph/sourcegraph/blob/184da4ce4ae21ca7a47c310a701356de2043d6b5/cmd/frontend/internal/app/jscontext/jscontext.go#L711-L715)
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## Changelog

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Audience: TS/CSE > Customers > Teammates (in that order).

Cheat sheet: $type = chore|fix|feat $domain:
source|search|ci|release|plg|cody|local|...
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Author: taras-yemets

client/web/src/cody/util.ts

@@ -13,8 +13,7 @@ export const manageSubscriptionRedirectURL = `${
  * for managing their Cody Pro subscription information.
  */
 export function isEmbeddedCodyProUIEnabled(): boolean {
-    return !!(window.context?.frontendCodyProConfig as { stripePublishableKey: string } | undefined)
-        ?.stripePublishableKey
+    return !!window.context.frontendCodyProConfig?.useEmbeddedUI
 }
 
 /**

client/web/src/jscontext.ts

@@ -314,6 +314,7 @@ export interface SourcegraphContext extends Pick<Required<SiteConfiguration>, 'e
     frontendCodyProConfig?: {
         stripePublishableKey: string
         sscBaseUrl: string
+        useEmbeddedUI: boolean
     }
 }
 

cmd/frontend/internal/app/jscontext/jscontext.go

@@ -153,6 +153,7 @@ type LicenseInfo struct {
 type FrontendCodyProConfig struct {
 	StripePublishableKey string `json:"stripePublishableKey"`
 	SscBaseUrl           string `json:"sscBaseUrl"`
+	UseEmbeddedUI        bool   `json:"useEmbeddedUI"`
 }
 
 // JSContext is made available to JavaScript code via the
@@ -710,5 +711,6 @@ func makeFrontendCodyProConfig(config *schema.CodyProConfig) *FrontendCodyProCon
 	return &FrontendCodyProConfig{
 		StripePublishableKey: config.StripePublishableKey,
 		SscBaseUrl:           config.SscBaseUrl,
+		UseEmbeddedUI:        config.UseEmbeddedUI,
 	}
 }

schema/schema.go

@@ -2279,6 +2279,11 @@
               "type": "string",
               "default": "https://accounts.sourcegraph.com/cody",
               "description": "The base URL of the Self-Serve Cody site."
+            },
+            "useEmbeddedUI": {
+              "type": "boolean",
+              "default": false,
+              "description": "Whether Cody Pro UI is served from sourcegraph.com. If false, users are directed to https://accounts.sourcegraph.com/cody to manage their Cody Pro subscription."
             }
           }
         }