(core) Billing updates

Summary:
- Adding confirmation dialog when user doesn't want to cancel site
- Changing `Cancel subscription` to `Cancel plan`
- Removing `Pro` from upgrade header on pricing modal
- Better handling situation when there is no default price
- Removing mentions about sprouts program
- Removing cache for stripe plans

Test Plan: Updated tests

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D4273

app/client/ui/HomeIntro.ts

@@ -83,7 +83,6 @@ function makeViewerTeamSiteIntro(homeModel: HomeModel) {
 }
 
 function makeTeamSiteIntro(homeModel: HomeModel) {
-  const sproutsProgram = cssLink({href: commonUrls.sproutsProgram, target: '_blank'}, t("Sprouts Program"));
   return [
     css.docListHeader(
       t("Welcome to {{- orgName}}", {orgName: homeModel.app.currentOrgName}),
@@ -94,8 +93,8 @@ function makeTeamSiteIntro(homeModel: HomeModel) {
     (!isFeatureEnabled('helpCenter') ? null :
       cssIntroLine(
         t(
-          'Learn more in our {{helpCenterLink}}, or find an expert via our {{sproutsProgram}}.',
-          {helpCenterLink: helpCenterLink(), sproutsProgram}
+          'Learn more in our {{helpCenterLink}}.',
+          {helpCenterLink: helpCenterLink()}
         ),
         testId('welcome-text')
       )

app/common/gristUrls.ts

@@ -93,7 +93,6 @@ export const commonUrls = {
   contactSupport: getContactSupportUrl(),
   termsOfService: getTermsOfServiceUrl(),
   plans: "https://www.getgrist.com/pricing",
-  sproutsProgram: "https://www.getgrist.com/sprouts-program",
   contact: "https://www.getgrist.com/contact",
   templates: 'https://www.getgrist.com/templates',
   community: 'https://community.getgrist.com',