[SPARK-28055][SS][DSTREAMS] Add delegation token custom AdminClient configurations.

[gaborgsomogyi]

What changes were proposed in this pull request?

At the moment Kafka delegation tokens are fetched through AdminClient but there is no possibility to add custom configuration parameters. In options there is already a possibility to add custom configurations.

In this PR I've added similar this possibility to AdminClient.

How was this patch tested?

Existing + added unit tests.

cd docs/
SKIP_API=1 jekyll build

Manual webpage check.

[gaborgsomogyi]

@koertkuipers the feature is on the way what we've spoken about. Ping me if you think this area lacks something.

[SparkQA]

Test build #106513 has finished for PR 24875 at commit 348c4ab.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[koertkuipers]

looks good to me

[gaborgsomogyi]

cc @vanzin

[koertkuipers]

this branch works for me to set ssl.endpoint.identification.algorithm to empty string for admin client

[gaborgsomogyi]

@koertkuipers Thanks for testing it!

[SparkQA]

Test build #107072 has finished for PR 24875 at commit 30e4dd1.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #107077 has finished for PR 24875 at commit 27fde79.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #107075 has finished for PR 24875 at commit 52467de.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[vanzin]

retest this please

[SparkQA]

Test build #107488 has finished for PR 24875 at commit 27fde79.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[vanzin]

Merging to master.