Update Tonemap docs in Environment and post-processing page

[allenwp]

Update Tonemap docs in Environment and post-processing page to include AgX and match 4.4.0 class reference.

Historically, this page has been not much more than a copy-paste of the tonemap class reference text, so this PR updates to match the latest for 4.4.0

After 4.5 introduces the White parameter for AgX, it will be a good time to revisit this section and rewrite it as supplementary text to the class reference, rather than duplicate text.

[tetrapod00]

For reference, godotengine/godot#102820 is the corresponding engine PR for this

I don't think that using *Note:* like this in the manual makes that much sense stylistically. Other than that, I didn't suggest any changes to the text, since this is mostly a copy-paste job.

[allenwp]

Agreed on all points @tetrapod00. I've pushed an update with all of your suggestions. (I favoured simply removing text in both cases where you suggested that as an option.)

[allenwp]

I'm getting these errors on the checks:

Run /home/runner/work/_actions/lycheeverse/lychee-action/v2/entrypoint.sh
   [WARN ] Cache is too old (age: 1d 0h 15m 17s, max age: 1d 0h 0m 0s). Discarding and recreating.
   [WARN ] Error creating request: InvalidBaseJoin("_static/")
   [WARN ] Error creating request: InvalidBaseJoin("res://someresource.res::1")
Error:  https://webd97.de/post/gitlab-pages-compression/ | Network error: error sending request for url (https://webd97.de/post/gitlab-pages-compression/) Maybe a certificate error?

## Errors per input

### Errors in tutorials/export/exporting_for_web.rst

Error: R] [https://webd97.de/post/gitlab-pages-compression/](https://webd97.de/post/gitlab-pages-compression/) | Network error: error sending request for url (https://webd97.de/post/gitlab-pages-compression/) Maybe a certificate error?

I tried re-running the checks, but that didn't resolve them. Let me know if this is something on my end that needs addressing...

[tetrapod00]

I'm getting these errors on the checks

Not your fault, it's bad links on unrelated pages. Helpfully someone already made an issue for it: #10717.

Looks like triggering the URL check on every PR means that we do get plenty of warning when something breaks 😄

[skyace65]

Thanks!