docs: fix typos and add spellcheck CI

[kashmeertl]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines

• What kind of change does this PR introduce?

/kind documentation
/kind cleanup

• What this PR does / why we need it:
  Fixes spelling and grammar mistakes in English docs (and matching versioned docs), corrects an invalid homepage Link key prop (KeyFeaturesy → key), and adds a cspell CI workflow so future docs/blog typos are caught automatically.

• Which issue(s) this PR fixes:
  docs: fix spelling and grammar issues across English pages #559

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[volcano-sh-bot]

Welcome @kashmeertl! It looks like this is your first PR to volcano-sh/website 🎉

[yashisrani]

@kashmeertl There is one commit incorrectly signed off. This means that the author of this commit failed to include a Signed-off-by line in the commit message.

To avoid having PRs blocked in the future, always include Signed-off-by: Author Name authoremail@example.com in every commit message. You can also do this automatically by using the -s flag (i.e., git commit -s).