* add a plain text email template
* use plain text email template for file based emails
* add config option to SMTP emails named disable_html_emails
* config option is a boolean that when set to true will only send plain text emails
* add docs for more complex SMTP notifier options
* update template
* add rfc1341 multipart logic to notifier
* check for errors after identity_verification
* * fix nil ptr
* go mod tidy
* remove needless checks
* * use multipart/atlernative instead
* * add rfc5322 compliant date header
* * fix linting issues
* [FIX] File Notifier Default Permissions
* set to 0600 for security
* recreate file if it exists with correct perms
* remove named return vars from notifier
* implement SMTP notifier startup check
* check dial, starttls, auth, mail from, rcpt to, reset, and quit
* log the error on failure
* implement mock
* misc optimizations, adjustments, and refactoring
* implement validate_skip config option
* fix comments to end with period
* fix suites that used smtp notifier without a smtp container
* add docs
* add file notifier startup check
* move file mode into const.go
* disable gosec linting on insecureskipverify since it's intended, warned, and discouraged
* minor PR commentary adjustment
* apply suggestions from code review
Co-Authored-By: Amir Zarrinkafsh <nightah@me.com>
