feat: change log level for token fetch message to debug (#294)

Fixes #293 and
provides some context where the message is coming from.

The OAuth2 M2M authenticator currently logs token fetch operations at
the Info level in auth/oauth/m2m/m2m.go at line 60. When running
applications with Info-level logging enabled, this generates log entries
every time a token is fetched or refreshed, which pollutes application
logs with operational noise. Its also messing with my Ginkgo tests in
CI: onsi/ginkgo#1614 (comment).
Libraries should generally avoid logging at Info level during normal
operations unless there's actionable information for the application
operator. I think this is a pretty standard practice.

Author: vikrantpuppala

auth/oauth/m2m/m2m.go

@@ -57,7 +57,7 @@ func (c *authClient) Authenticate(r *http.Request) error {
 
 	c.tokenSource = GetTokenSource(config)
 	token, err := c.tokenSource.Token()
-	log.Debug().Msgf("token fetched successfully")
+	log.Debug().Msgf("databricks OAuth token fetched successfully")
 	if err != nil {
 		log.Err(err).Msg("failed to get token")