Style corrections for word choice

Update words to bring closer to GitLab style. Add words to the
spelling exceptions document.

.markdownlint.json

@@ -59,6 +59,7 @@
       "GitLab Shell",
       "GitLab Workhorse",
       "GitLab",
+      "Gitleaks",
       "Gmail",
       "Google",
       "Grafana",
@@ -114,6 +115,7 @@
       "Shibboleth",
       "Slack",
       "SMTP",
+      "SpotBugs",
       "SSH",
       "Tiller",
       "TOML",

doc/.vale/gitlab/spelling-exceptions.txt

@@ -101,6 +101,7 @@ failovers
 failsafe
 favicon
 firewalled
+Flawfinder
 Flowdock
 Fluentd
 Forgerock
@@ -112,9 +113,11 @@ Gitea
 GitHub
 GitLab
 gitlabsos
+Gitleaks
 Gitter
 Gmail
 Google
+Gosec
 Gradle
 Grafana
 gravatar
@@ -160,6 +163,7 @@ Kibana
 Knative
 Kramdown
 Kubernetes
+Kubesec
 Laravel
 LDAP
 Libravatar
@@ -305,9 +309,11 @@ serializing
 Slack
 Slony
 SMTP
+Sobelow
 Sourcegraph
 spidering
 Splunk
+SpotBugs
 SSH
 storable
 strace