docs: Add EXPLAIN CREATE TABLE documentation

[garimauttam]

Resolves #27148

Changes

Added EXPLAIN CREATE TABLE syntax to explain.rst
Add examples including IF NOT EXISTS
Clarify that EXPLAIN returns a summary and does not execute the DDL

== NO RELEASE NOTE ==

[sourcery-ai]

🧙 Sourcery has finished reviewing your pull request!

---

Tips and commands

Interacting with Sourcery

• Trigger a new review: Comment @sourcery-ai review on the pull request.
• Continue discussions: Reply directly to Sourcery's review comments.
• Generate a GitHub issue from a review comment: Ask Sourcery to create an
  issue from a review comment by replying to it. You can also reply to a
  review comment with @sourcery-ai issue to create an issue from it.
• Generate a pull request title: Write @sourcery-ai anywhere in the pull
  request title to generate a title at any time. You can also comment
  @sourcery-ai title on the pull request to (re-)generate the title at any time.
• Generate a pull request summary: Write @sourcery-ai summary anywhere in
  the pull request body to generate a PR summary at any time exactly where you
  want it. You can also comment @sourcery-ai summary on the pull request to
  (re-)generate the summary at any time.
• Generate reviewer's guide: Comment @sourcery-ai guide on the pull
  request to (re-)generate the reviewer's guide at any time.
• Resolve all Sourcery comments: Comment @sourcery-ai resolve on the
  pull request to resolve all Sourcery comments. Useful if you've already
  addressed all the comments and don't want to see them anymore.
• Dismiss all Sourcery reviews: Comment @sourcery-ai dismiss on the pull
  request to dismiss all existing Sourcery reviews. Especially useful if you
  want to start fresh with a new review - don't forget to comment
  @sourcery-ai review to trigger a new review!

Customizing Your Experience

Access your dashboard to:

• Enable or disable review features such as the Sourcery-generated pull request
  summary, the reviewer's guide, and others.
• Change the review language.
• Add, remove or edit custom review instructions.
• Adjust other review settings.

Getting Help

• Contact our support team for questions or feedback.
• Visit our documentation for detailed guides and information.
• Keep in touch with the Sourcery team by following us on X/Twitter, LinkedIn or GitHub.

[sourcery-ai]

Hey - I've reviewed your changes and they look great!

---

Sourcery is free for open source - if you like our reviews please consider sharing them ✨

• X
• Mastodon
• LinkedIn
• Facebook

_{Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.}

[steveburnett]

LGTM! (docs)

Pull branch, local doc build, looks good. Thanks!

[steveburnett]

The CI checks seem to be stuck in pending status. You may need to re-push the branch to re-run the CI checks. If you do that, re-request a review from me and I'll be happy to approve this again so it can be merged.

[steveburnett]

LGTM! (docs)

Pull updated branch, new local doc build, looks good. Thanks!

[steveburnett]

The CI block for docs-only PRs has been fixed in #27285. Could you rebase to the latest master branch? Then we can move forward and merge this PR.

Please add

== NO RELEASE NOTE ==

to the PR description.

[steveburnett]

LGTM! (docs)

Pull updated branch, new local doc build, looks good. Thanks!