feat [python]: Add getter/setter property for writer_bucket_no_key_assigner config

[charlesdong1991]

After my previous PR for updating writer_bucket_no_key_assigner config, I realize unlike other configs, this config does not have getter/setter property.

So this PR adds it up. No tests should be needed.

[charlesdong1991]

@luoyuxia @fresh-borzoni @leekeiabstraction PTAL. Thanks!

[fresh-borzoni]

@charlesdong1991 TY for the PR

Small comment:
The same match value { "round_robin" | "sticky" } now exists in 3 places (dict constructor, this setter, Cpp new_connection). NoKeyAssigner already derives ValueEnum but is missing FromStr.

strum is already a dep and DataLakeFormat already uses the exact pattern needed, we can do like this:

  #[derive(..., EnumString, Display)]                                                                                                                                                                                                                
  #[strum(ascii_case_insensitive)]                      
  pub enum NoKeyAssigner {
      #[strum(serialize = "sticky")]
      Sticky,
      #[strum(serialize = "round_robin")]
      RoundRobin,
  }

Then all 3 sites become value.parse().map_err(...) — same as the numeric fields. Also makes parsing case-insensitive for free.

[charlesdong1991]

Good call, we can indeed de-duplicate and clean codebase! @fresh-borzoni 👍

[charlesdong1991]

I did the changes, please let me know if any further changes! Thanks again! @fresh-borzoni

[fresh-borzoni]

@charlesdong1991 Ty, LGTM

[leekeiabstraction]

Ty for the pr!