Update CLI Reference with --site & --base flags

[natemoo-re]

What kind of changes does this PR include?

• New or updated content

Description

• Adds missing --site flag to CLI reference, which has been supported for a long time.
• Adds new --base flag to CLI reference, which is implemented in Add support for --base CLI argument astro#4917

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[sarah11918]

LGTM, @natemoo-re! Just to make sure docs are coordinated with the feature release properly, because --site already exists, but --base is new, and not yet released...

Either this PR needs to wait on the upstream PR withastro/astro#4917 to merge, and we can apply the merge-on-release label to remind us to wait. OR

We can use the <Since /> component to specify the version of Astro that --base works with (even if it's a future version) and it's less of a concern if Docs are merged before the feature is released. This would look like:

---
setup: |
  import Since from '~/components/Since.astro';
 ---
### `--base`

<Since v="1.4.0" />

(Might we want to do this anyway, in case people on older versions try to use --base ?)

[natemoo-re]

Great catch, @sarah11918! Added the Since label for --base.

[delucis]

Looks good Nate! One comment with how we show these headings. Not entirely happy with my proposed argument names, happy for you to change those if you think something else would be better. (Edit: just saw your naming in the upstream PR and adjusted accordingly.)

[delucis]

Do these need to indicate the arguments they get passed like we do for --root and --config?

Suggested change

	### `--site`
	### `--site <url>`

[delucis]

Suggested change

	### `--base`
	### `--base <pathname>`

[delucis]

(added the flags to the PR title so we can test #1653)