Self-hosted in-product purchase (#21804)

* Self-hosted admins can purchase licenses in-app when `ServiceSettings,SelfHostedPurchase` is true (the default)
* Content Security Policy enables loading assets from `js.stripe.com/v3` when `ServiceSettings.SelfHostedPurchase` is true (the default).
* Add `hosted_customer` API subpath
* Add status of SelfHostedPurchase to telemetry config report.
* Support showing admins self-hosted invoices when `ServiceSettings.SelfHostedPurchase` is true (the default)

Co-authored-by: Conor Macpherson <116016004+ConorMacpherson@users.noreply.github.com>

services/telemetry/telemetry.go

@@ -455,7 +455,7 @@ func (ts *TelemetryService) trackConfig() {
 		"restrict_link_previews":                                  isDefault(*cfg.ServiceSettings.RestrictLinkPreviews, ""),
 		"enable_custom_groups":                                    *cfg.ServiceSettings.EnableCustomGroups,
 		"post_priority":                                           *cfg.ServiceSettings.PostPriority,
-		"self_hosted_first_time_purchase":                         *cfg.ServiceSettings.SelfHostedFirstTimePurchase,
+		"self_hosted_purchase":                                    *cfg.ServiceSettings.SelfHostedPurchase,
 		"allow_synced_drafts":                                     *cfg.ServiceSettings.AllowSyncedDrafts,
 	})