Adding Upgrade to Enterprise version feature (#14539)

* Adding Upgrade to Enterprise version feature

* Addressing PR review comments, and adding some minor improvements

* Add tests file

* Addressing PR comments

* fix linter checks

* Storing and exposing the upgraded from TE info

* Fix showing errors on mac

* A more appropiate status code for not-supported upgrade

* Fixing tests

* Handling permissions errors

* More server logging around upgrade failures

* Apply text changes suggested from code review

Co-authored-by: Eric Sadur <57730300+esadur@users.noreply.github.com>

* Address PR review comments

* Only allow to restart the system after an upgrade

* Verify file signature before upgrade

* Adding limit to the downloaded file

* Simplifying the upgrade binary process with backup in memory

* Fixing backup/restore mechanism for the binary file

* Improve file permissions handling

* Askin the permissions for the right place (the parent directory)

* Fixing tests

* Addressing PR review comments

* Fix license headers

* Fixing retry layer

* Making it work on windows builds

* Adding license header

* Fixing 2 tests

* Fixing tests that need UpgradeFromTE System key mock

* Extracting i18n translation

* Apply suggestions from code review

Co-authored-by: Eric Sadur <57730300+esadur@users.noreply.github.com>

* Improving how the errors are written

* Fixing another error text

* Removing unneeded translation

* Fixing upgrade status strings

* Update i18n/en.json

Co-authored-by: Eric Sadur <57730300+esadur@users.noreply.github.com>

* Fixing tests

Co-authored-by: Eric Sadur <57730300+esadur@users.noreply.github.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/config.go

@@ -346,6 +346,7 @@ func (s *Server) ClientConfigWithComputed() map[string]string {
 	// by the client.
 	respCfg["NoAccounts"] = strconv.FormatBool(s.IsFirstUserAccount())
 	respCfg["MaxPostSize"] = strconv.Itoa(s.MaxPostSize())
+	respCfg["UpgradedFromTE"] = strconv.FormatBool(s.isUpgradedFromTE())
 	respCfg["InstallationDate"] = ""
 	if installationDate, err := s.getSystemInstallDate(); err == nil {
 		respCfg["InstallationDate"] = strconv.FormatInt(installationDate, 10)