Add Grails 8 email guide (v8 prose, snippets, guides.yml)

[sanjana2505006]

Adds the Grails 8 email guide under guides/grails-email/v8/ (AsciiDoc chapters + vendored snippets) and registers the v8 version in conf/guides.yml with TOC.

Companion to grails-guides/grails-email#1

[jamesfredley]

Thanks @sanjana2505006! Reviewed the v8 email guide prose plus conf/guides.yml. The good news first: all 12 TOC keys map to chapter files (no orphans), and every include:: snippet path resolves to a vendored snippet. A few things to address before merge. The publication date is fine, please ignore that one.

Inline comments below cover: the guides.yml TOC syntax and author name, the SMTP config filename mismatch, and the injected == Verify CI heading.

One cross-cutting item that is not line-specific:

• Typography: please remove em/en dashes (the — character) throughout. They appear in the subtitle (guides.yml), introduction.adoc (line 1), gettingStarted.adoc (line 17), and summary.adoc (line 7). Replace them with commas, colons, parentheses, or regular hyphens per project style.

• SMTP config filename (cross-PR): the biggest item is that the mail-config filename must be identical in three places: the sample app (companion PR grails-guides/grails-email#1 currently names it application-development.yml), the vendored snippet here (application-email.yml), and the prose/caption (application.yml). Please reconcile to a single name across both PRs. Details in the inline comment on smtpMail.adoc.

[sanjana2505006]

@jamesfredley I've updated the code
please have a look and let me know if there's anything else i can do

[jamesfredley]

Latest-head re-review: the original feedback is addressed, and I resolved those prior threads. validateGuides -PvalidationMode=both passes and the targeted guide renders and loads cleanly.

A new blocking cross-PR drift remains: the vendored snippets no longer match the companion sample-app head. In particular:

• resources.groovy still uses AwsSesMailService and silently routes unknown providers to SMTP.
• SendGridEmailService.groovy still drops the HTML alternative and swallows provider failures.
• AwsSesMailService.groovy retains the old class name and swallows SES failures.
• MailController.groovy still returns a bare 422.
• MailControllerSpec.groovy lacks the added invalid-request cases.

Please fix the remaining companion-PR blockers first, then re-vendor these files from that corrected head and update the AWS filename/include to AwsSesEmailService.groovy.

[sanjana2505006]

@jamesfredley, addressed the inline notes.
Please have another look whenever you get a chance and let me know if there's any other requirements

[jamesfredley]

This snippet is still the pre-b07505d implementation: it warns and continues when aws.ses.source is missing, and bodyOfEmail still drops the text alternative whenever HTML is present. Please re-vendor the final companion implementation after the sample PR is green; it must fail fast on missing source and preserve both text and HTML.

[jamesfredley]

The guide still publishes cmd.toString() at INFO, which includes recipient, CC/BCC, subject, and both message bodies. Please re-vendor the final privacy-safe controller from the companion app after its logging fix is complete.

[jamesfredley]

This vendored test remains behind the companion head: it still compares against UNPROCESSABLE_ENTITY and only checks that path/links are truthy. Please re-vendor the final green test after the sample app correctly returns and asserts exact /mail/send path and self-link values.

[jamesfredley]

The guide previously leaves the reader in grails-email/initial, so this command targets a nonexistent initial/complete directory. Please use cd ../complete, consistent with the corrected Getting Started chapter.