Spaced conf keys escape exact-key redaction in logged engine commands

### Describe the bug

`genKeyValuePair` assembles a `key=value` command-line argument by trimming only the concatenated string:

```scala
def genKeyValuePair(key: String, value: String): String = s"$key=$value".trim
```

`.trim` on the whole string strips the outer ends but leaves any whitespace between the key and the value. `genKeyValuePair("abc ", "123")` returns `"abc =123"`, with the space kept before the `=`, so the trim the method advertises is only half applied.

This has a concrete consequence for secret redaction. `redactConfValues` splits each assembled argument on `=` and matches the key against an exact key set. When a conf key carries stray whitespace, the assembled argument is `" ="`, so the extracted key `" "` misses the exact set and the value is not redacted.

The gap is reachable for the Data Agent engine's API key. `kyuubi.engine.data.agent.openai.api.key` is not matched by the default pattern-based redaction (`secret|password|token|access.key`), so exact-key redaction is the only stage that would mask it. Session conf keys are not trimmed on the way through, so a key submitted with a trailing space escapes that stage and the API key value lands in the engine launch command written to the server log.

### Affects Version(s)

master (1.13.0-SNAPSHOT), and earlier releases carrying `kyuubi-util-scala`.

### Are you willing to submit PR?

Yes.

Start by locating genKeyValuePair and redactConfValues in the kyuubi-util-scala code, then inspect the existing tests for command assembly and configuration redaction. Reproduce a key with trailing whitespace and verify that exact-key values, including the Data Agent API key, are masked in the logged engine command.

Written by the indexing model from the issue text.