GH-40441: [GLib][Docs] Use Sphinx for Apache Arrow GLib front page

[kou]

Rationale for this change

Using both of apache/arrow and apache/arrow-site to maintain https://arrow.apache.org/docs/c_glib/ is difficult to maintain.

What changes are included in this PR?

Use https://github.com/apache/arrow/tree/main/docs/source/c_glib as https://arrow.apache.org/docs/c_glib/ 's source.

Are these changes tested?

Yes.

Are there any user-facing changes?

Yes.

• GitHub Issue: [GLib][Docs] Use Sphinx for Apache Arrow GLib front page #40441

[kou]

@github-actions crossbow submit preview-docs

[github-actions]

⚠️ GitHub issue #40441 has been automatically assigned in GitHub to PR creator.

[github-actions]

Revision: 1d32a42

Submitted crossbow builds: ursacomputing/crossbow @ actions-a989531c52

Task	Status
preview-docs

[kou]

@AlenkaF @jorisvandenbossche Can we enable MyST-Parser to use Markdown in Sphinx?

[jorisvandenbossche]

I am certainly fine with that, yes

[AlenkaF]

Me too 👍

[kou]

Thanks!

I'll merge this.

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 5 benchmarking runs that have been run so far on merge-commit 1eb46f7.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 8 possible false positives for unstable benchmarks that are known to sometimes produce them.

[kou]

@github-actions crossbow submit preview-docs

[github-actions]

Revision: 7ab6a3e

Submitted crossbow builds: ursacomputing/crossbow @ actions-20569c1b70

Task	Status
preview-docs

[kou]

http://crossbow.voltrondata.com/pr_docs/40442/python/generated/pyarrow.schema.html