[DOP-25329] Use SecretStr for cookie secret_key #1320

Job	Run time
Oracle tests / Run Oracle tests	4m 28s
MySQL tests / Run MySQL tests	3m 53s
Clickhouse tests / Run Clickhouse tests	4m 43s
Hive tests / Run Hive tests	4m 18s
S3 tests / Run S3 tests	7m 43s
FTP tests / Run FTP tests	6m 34s
Unit tests / Run unit tests	3m 9s
Samba tests / Run Samba tests	4m 0s
FTPS tests / Run FTPS tests	3m 46s
Scheduler tests / Run Scheduler tests	1m 28s
SFTP tests / Run SFTP tests	3m 35s
MSSQL tests / Run MSSQL tests	3m 57s
HDFS tests / Run HDFS tests	7m 37s
WebDAV tests / Run WebDAV tests	4m 5s
Tests done	21s
	1h 3m 37s

Provide feedback