Fix config Sanitize fields missing from desanitize, causing FakeSetting to be persisted (#36619) (#36653)

* Add TestDesanitizeRemovesAllFakeSettings to catch future omissions

Walks every string field in the config after a Sanitize+desanitize
round-trip and fails if any still holds FakeSetting. This catches the
case where a field is added to Sanitize without a corresponding
desanitize entry.

* Fix ElasticsearchSettings.ClientKey being incorrectly masked as a secret

ClientKey is a file path, not a secret value. Masking it caused the
asterisk string to be persisted to the database on config writes, which
broke TLS client auth on restart.

* Fix desanitize missing entries for fields added in 504fb96fdd98

504fb96fdd98 masked five fields in Sanitize without adding the
corresponding desanitize entries, meaning a config save through the
API would permanently overwrite those fields with FakeSetting:

- FileSettings.ExportAmazonS3SecretAccessKey
- ServiceSettings.GoogleDeveloperKey
- ServiceSettings.GiphySdkKey
- CacheSettings.RedisPassword
- AutoTranslationSettings.LibreTranslate.APIKey

* fixup! Add TestDesanitizeRemovesAllFakeSettings to catch future omissions

* fixup! Fix desanitize missing entries for fields added in 504fb96fdd98

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/config.go

@@ -4884,10 +4884,6 @@ func (o *Config) Sanitize(pluginManifests []*Manifest, opts *SanitizeOptions) {
 		*o.ElasticsearchSettings.Password = FakeSetting
 	}
 
-	if o.ElasticsearchSettings.ClientKey != nil && *o.ElasticsearchSettings.ClientKey != "" {
-		*o.ElasticsearchSettings.ClientKey = FakeSetting
-	}
-
 	for i := range o.SqlSettings.DataSourceReplicas {
 		o.SqlSettings.DataSourceReplicas[i] = sanitizeDataSourceField(o.SqlSettings.DataSourceReplicas[i], "SqlSettings.DataSourceReplicas")
 	}