MM-53879: Fix recursive loading of license (#24200)

There were multiple problems with loading of a license.

1. It was called from inside app/server.go and app/platform/service.go. The first one wasn't really needed anymore, so we remove it.

2. To make loading of a license work across a cluster, the license load action was attached along with the `InvalidateAllCachesSkipSend` method. But the problem with that was that it would even get called in the caller node as well, putting it in a recursive loop.

```
LoadLicense -> SaveLicense -> InvalidateAllCaches -> InvalidateAllCachesSkipSend -> LoadLicense
```

To fix this, we create a dedicated loadLicense cluster event and move it away from the `InvalidateAllCachesSkipSend` method. And then from the caller side, we just trigger this action.

3. We also remove the first call to check license expiration which would load the license again. This is unnecessary because if the license is expired, server wouldn't start at all.

While here, we also make some other improvements like removing unnecessary goroutine spawning while publishing websocket events. They are already handled asynchronously, so there is no need
to create a goroutine for that.

We also remove

```
ps.ReloadConfig()
ps.InvalidateAllCaches()
```

from requestTrialLicense as they are already called from inside `*PlatformService.SaveLicense`.

And lastly, we remove the `*model.AppError` return from `*PlatformService.InvalidateAllCaches` because there was nothing to return at all.

https://mattermost.atlassian.net/browse/MM-53879

```release-note
Fix several issues with loading of a license
```

server/channels/app/license_test.go

@@ -1,109 +0,0 @@
-// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
-// See LICENSE.txt for license information.
-
-package app
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-
-	"github.com/mattermost/mattermost/server/public/model"
-)
-
-func TestLoadLicense(t *testing.T) {
-	th := Setup(t)
-	defer th.TearDown()
-
-	th.App.Srv().LoadLicense()
-	require.Nil(t, th.App.Srv().License(), "shouldn't have a valid license")
-}
-
-func TestSaveLicense(t *testing.T) {
-	th := Setup(t)
-	defer th.TearDown()
-
-	b1 := []byte("junk")
-
-	_, err := th.App.Srv().SaveLicense(b1)
-	require.NotNil(t, err, "shouldn't have saved license")
-}
-
-func TestRemoveLicense(t *testing.T) {
-	th := Setup(t)
-	defer th.TearDown()
-
-	err := th.App.Srv().RemoveLicense()
-	require.Nil(t, err, "should have removed license")
-}
-
-func TestSetLicense(t *testing.T) {
-	th := Setup(t)
-	defer th.TearDown()
-
-	l1 := &model.License{}
-	l1.Features = &model.Features{}
-	l1.Customer = &model.Customer{}
-	l1.StartsAt = model.GetMillis() - 1000
-	l1.ExpiresAt = model.GetMillis() + 100000
-	ok := th.App.Srv().SetLicense(l1)
-	require.True(t, ok, "license should have worked")
-
-	l3 := &model.License{}
-	l3.Features = &model.Features{}
-	l3.Customer = &model.Customer{}
-	l3.StartsAt = model.GetMillis() + 10000
-	l3.ExpiresAt = model.GetMillis() + 100000
-	ok = th.App.Srv().SetLicense(l3)
-	require.True(t, ok, "license should have passed")
-}
-
-func TestGetSanitizedClientLicense(t *testing.T) {
-	th := Setup(t)
-	defer th.TearDown()
-
-	setLicense(th, nil)
-
-	m := th.App.Srv().GetSanitizedClientLicense()
-
-	_, ok := m["Name"]
-	assert.False(t, ok)
-	_, ok = m["SkuName"]
-	assert.False(t, ok)
-}
-
-func TestGenerateRenewalToken(t *testing.T) {
-	th := Setup(t)
-	defer th.TearDown()
-
-	t.Run("renewal token generated correctly", func(t *testing.T) {
-		setLicense(th, nil)
-		token, appErr := th.App.Srv().GenerateRenewalToken(JWTDefaultTokenExpiration)
-		require.Nil(t, appErr)
-		require.NotEmpty(t, token)
-	})
-
-	t.Run("return error if there is no active license", func(t *testing.T) {
-		th.App.Srv().SetLicense(nil)
-		_, appErr := th.App.Srv().GenerateRenewalToken(JWTDefaultTokenExpiration)
-		require.NotNil(t, appErr)
-	})
-}
-
-func setLicense(th *TestHelper, customer *model.Customer) {
-	l1 := &model.License{}
-	l1.Features = &model.Features{}
-	if customer != nil {
-		l1.Customer = customer
-	} else {
-		l1.Customer = &model.Customer{}
-		l1.Customer.Name = "TestName"
-		l1.Customer.Email = "test@example.com"
-	}
-	l1.SkuName = "SKU NAME"
-	l1.SkuShortName = "SKU SHORT NAME"
-	l1.StartsAt = model.GetMillis() - 1000
-	l1.ExpiresAt = model.GetMillis() + 100000
-	th.App.Srv().SetLicense(l1)
-}