Transfer engine pool name to lower case

[turboFei]

Why are the changes needed?

1. engine pool name is used to build the subdomain.
2. the subdomain is case-insensitive
3. however, now, the engine pool name is case sensitive
4. when we try to delete the engine with subdomain(enginePool-index), it failed to find the zookeeper path

kyuubi/kyuubi-common/src/main/scala/org/apache/kyuubi/config/KyuubiConf.scala

Lines 2363 to 2369 in bebe10a

	@deprecated("using kyuubi.engine.share.level.subdomain instead", "1.4.0")
	val ENGINE_SHARE_LEVEL_SUB_DOMAIN: ConfigEntry[Option[String]] =
	buildConf("kyuubi.engine.share.level.sub.domain")
	.doc("(deprecated) - Using kyuubi.engine.share.level.subdomain instead")
	.version("1.2.0")
	.stringConf
	.transformToLowerCase

FYI:
Unable to delete the engine zk node with engine pool mode.

How was this patch tested?

UT.

Was this patch authored or co-authored using generative AI tooling?

No.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (3b205a3) to head (7cbe255).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #7241   +/-   ##
======================================
  Coverage    0.00%   0.00%           
======================================
  Files         696     696           
  Lines       43530   43530           
  Branches     5883    5883           
======================================
  Misses      43530   43530           

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[turboFei]

thanks, merged to 1.10.3 and 1.11.0