Add smtp to start_tls values

Author: jake-walker

tls/assets/configuration/spec.yaml

@@ -146,5 +146,6 @@ files:
         enum:
         - postgres
         - mysql
+        - smtp
     - template: instances/default
     - template: instances/tls

tls/datadog_checks/tls/config_models/instance.py

@@ -53,7 +53,7 @@ class InstanceConfig(BaseModel):
     server: str
     server_hostname: Optional[str] = None
     service: Optional[str] = None
-    start_tls: Optional[Literal['postgres', 'mysql']] = None
+    start_tls: Optional[Literal['postgres', 'mysql', 'smtp']] = None
     tags: Optional[tuple[str, ...]] = None
     timeout: Optional[int] = None
     tls_ca_cert: Optional[str] = None

tls/datadog_checks/tls/data/conf.yaml.example

@@ -133,7 +133,7 @@ instances:
     ## irc, postgres, mysql, lmtp, nntp, sieve, and ldap.
     ##
     ## Currently this checks supports only the below protocols:
-    ##   postgres, mysql
+    ##   postgres, mysql, smtp
     #
     # start_tls: <START_TLS>
 
@@ -222,8 +222,8 @@ instances:
     # tls_validate_hostname: true
 
     ## @param tls_ciphers - list of strings - optional
-    ## The list of ciphers suites to use when connecting to an endpoint. If not specified, 
-    ## `ALL` ciphers are used. For list of ciphers see: 
+    ## The list of ciphers suites to use when connecting to an endpoint. If not specified,
+    ## `ALL` ciphers are used. For list of ciphers see:
     ## https://www.openssl.org/docs/man1.0.2/man1/ciphers.html
     #
     # tls_ciphers: