fix: Infer TLS based on scheme of server string

[vcrfxia]

Description

This PR builds on top of #4891, which attempts to fix #4885.

The changes in #4891 reveal another bug:
The client props passed by the CLI to the rest client come from:

ksql/ksqldb-cli/src/main/java/io/confluent/ksql/Ksql.java

Line 124 in b0669a0

final Map<String, String> clientProps = PropertiesUtil.applyOverrides(configProps, systemProps);

and are immutable:

ksql/ksqldb-common/src/main/java/io/confluent/ksql/properties/PropertiesUtil.java

Line 95 in b0669a0

return ImmutableMap.copyOf(merged);

which means a java.lang.UnsupportedOperationException is thrown when the code tries to execute

clientProps.put(KsqlClient.TLS_ENABLED_PROP_NAME, "true");

as in #4891.

This PR works around that by copying the immutable map, and also updates unit and integration tests so similar issues don't reappear in the future.

Testing done

Manually verification that this fixes #4885

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")