docs: fix spelling and grammar issues across English pages

[kashmeertl]

Summary

Some documentation pages contain minor spelling and grammar issues that reduce readability. While a few are simple typos, others are wording or grammar mistakes that are not typically caught by basic spell checkers.

Examples

Spelling

• docs/Contribution/communitymembership.md: backword → backward

Grammar / Wording

• docs/GettingStarted/Tutorials.md: "A Kubernetes cluster ... need" → "needs"

• docs/Ecosystem/SparkOnVolcano.md: "clustering computing" → "cluster computing"

• docs/UserGuide/user_guide_how_to_enable_dra.md

• docs/KeyFeatures/UnifiedScheduling.md

  • "a example" → "an example"
  • "as your need" → "as needed"

Scope

• Fix the listed spelling and grammar issues in docs/
• Update matching files in versioned_docs/ where applicable
• Avoid changing API names, CRD fields, or other identifiers
• Optionally fix other obvious spelling/grammar issues found in the same files