Clarify documentation of SKIP_VERIFY (#12203)

* Clarify documentation of SKIP_VERIFY

The documentation clearly documents the empty value as the default,
however at least one user reported this as being unclear. Mark values
explicitly so it is clear what values it can take. This clarifies that
an empty value in fact leaves certificate verification enabled, whereas
it has to be explicitly set to true to disable certificate verification.

Resolves: #12117

Signed-off-by: Alexander Scheel <alexander.m.scheel@gmail.com>

* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

Co-authored-by: mrsdizzie <info@mrsdizzie.com>

* Update custom/conf/app.example.ini

Co-authored-by: mrsdizzie <info@mrsdizzie.com>

* Update custom/conf/app.example.ini

Co-authored-by: mrsdizzie <info@mrsdizzie.com>

Co-authored-by: mrsdizzie <info@mrsdizzie.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

custom/conf/app.example.ini

@@ -643,8 +643,8 @@ HOST =
 DISABLE_HELO =
 ; Custom hostname for HELO operation, if no value is provided, one is retrieved from system.
 HELO_HOSTNAME =
-; Do not verify the certificate of the server. Only use this for self-signed certificates
-SKIP_VERIFY =
+; Whether or not to skip verification of certificates; `true` to disable verification. This option is unsafe. Consider adding the certificate to the system trust store instead.
+SKIP_VERIFY = false
 ; Use client certificate
 USE_CERTIFICATE = false
 CERT_FILE = custom/mailer/cert.pem

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -408,7 +408,8 @@ set name for unique queues. Individual queues will default to
 - `USER`: **\<empty\>**: Username of mailing user (usually the sender's e-mail address).
 - `PASSWD`: **\<empty\>**: Password of mailing user.  Use \`your password\` for quoting if you use special characters in the password.
    - Please note: authentication is only supported when the SMTP server communication is encrypted with TLS (this can be via `STARTTLS`) or `HOST=localhost`. See [Email Setup]({{< relref "doc/usage/email-setup.en-us.md" >}}) for more information.
-- `SKIP_VERIFY`: **\<empty\>**: Do not verify the self-signed certificates.
+- `SKIP_VERIFY`: **false**: Whether or not to skip verification of certificates; `true` to disable verification.
+   - **Warning:** This option is unsafe. Consider adding the certificate to the system trust store instead.
    - **Note:** Gitea only supports SMTP with STARTTLS.
 - `SUBJECT_PREFIX`: **\<empty\>**: Prefix to be placed before e-mail subject lines.
 - `MAILER_TYPE`: **smtp**: \[smtp, sendmail, dummy\]