[DOP-23122] Use async methods of Keycloak client #1442

Job	Run time
MySQL tests / Run MySQL tests	1m 29s
Clickhouse tests / Run Clickhouse tests	1m 30s
Oracle tests / Run Oracle tests	1m 28s
HDFS tests / Run HDFS tests	1m 28s
MSSQL tests / Run MSSQL tests	1m 28s
Hive tests / Run Hive tests	1m 29s
FTP tests / Run FTP tests	1m 29s
SFTP tests / Run SFTP tests	1m 28s
Samba tests / Run Samba tests	1m 28s
Unit tests / Run unit tests	1m 30s
WebDAV tests / Run WebDAV tests	1m 31s
Scheduler tests / Run Scheduler tests	1m 28s
FTPS tests / Run FTPS tests	1m 29s
S3 tests / Run S3 tests	1m 30s
Tests done	1s
	20m 46s

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