Build: Downgrade hadoop version to 3.3.4 for Spark 3.x compatibility

[steveloughran]

• Downgrades the hadoop version
• Adds a comment to libs.versions saying why it needs to be kept down and hence when it can be upgraded.

Fixes #15100

[manuzhang]

I'm not sure this is worth it given

1. We've released iceberg with hadoop 3.4 and Spark 3.4 support since 1.7
2. Spark 3.4 support is already deprecated and we will remove after next release.

[steveloughran]

I'd like to get the bulk delete work of #10233 in, with the resulting 1000x speedup in performance in deleting files, but can't get the direct-API-invocation in without breaking spark 3.4.

Forcing the downgrade not only means I can return to the reflection-based binding.

There's also that risk of accidental overloads, enum/option use etc with any change made using hadoop apis stop working, even if previous releases were all OK

[manuzhang]

I'd like to get the bulk delete work of #10233 in, with the resulting 1000x speedup in performance in deleting files, but can't get the direct-API-invocation in without breaking spark 3.4.

Can we hold it till dropping Spark 3.4 support?