fix: enable ASF nextgen config

[Yicong-Huang]

What changes were proposed in this PR?

Enable the ASF .asf.yaml next-generation parser by adding meta.nextgen: true.

This lets ASF Infra apply repository feature settings that are already present in this file, including github.features.discussions: true.

Any related issues, documentation, discussions?

Related mailing list discussion: https://lists.apache.org/thread/hso97tz18zd6s9zpbr1gfj2o7m5rcr92

ASF Infra documentation:

• https://infra.apache.org/blog/newsletter_02_25.html
• https://github.com/apache/infrastructure-asfyaml/tree/ng-parser?tab=readme-ov-file#repository-features

How was this PR tested?

ruby -e 'require "yaml"; YAML.load_file(".asf.yaml"); puts "YAML OK"'
gh api repos/apache/texera --jq '{has_discussions:.has_discussions, default_branch:.default_branch, full_name:.full_name}'

The YAML parses successfully. The GitHub API check currently reports has_discussions: false, confirming the repository feature still needs ASF Infra to apply the updated .asf.yaml config after merge.

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

Generated-by: OpenAI Codex

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.17%. Comparing base (538ae1d) to head (45f815b).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #5139   +/-   ##
=========================================
  Coverage     43.17%   43.17%           
- Complexity     2213     2214    +1     
=========================================
  Files          1045     1045           
  Lines         40363    40363           
  Branches       4268     4268           
=========================================
+ Hits          17425    17426    +1     
+ Misses        21865    21862    -3     
- Partials       1073     1075    +2     

Flag	Coverage Δ
access-control-service	39.53% <ø> (ø)
agent-service	33.72% <ø> (ø)
amber	43.82% <ø> (+0.01%)	⬆️
computing-unit-managing-service	0.00% <ø> (ø)
config-service	0.00% <ø> (ø)
file-service	32.18% <ø> (ø)
frontend	34.07% <ø> (ø)
python	90.50% <ø> (ø)
workflow-compiling-service	56.81% <ø> (ø)

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