Add templating coalesce function (#4492)

website/content/docs/concepts/domain-model/credential-libraries.mdx

@@ -105,14 +105,21 @@ This value may not be populated, or it may be different from the account name us
 - `{{.Account.Subject}}` - The account's subject, if a subject is used by that type of account.
 - `{{.Account.Email}}` - The account's email, if email is used by that type of account.
 
-Additionally, there is currently a single function that strips the rest of a string after a specified substring.
-This function is useful for pulling a user or account name from an email address.
-The following example turns `foo@example.com` into `foo`:
+Additionally, there are a couple of useful functions:
+
+The `trucateFrom` function strips the rest of a string after a specified
+substring. This function is useful for pulling a user or account name from an
+email address. The following example turns `foo@example.com` into `foo`:
 
 `{{truncateFrom .Account.Email "@"}}`
 
 The example above uses the account email, but it could be any other parameter.
 
+The `coalesce` function chooses the first non-empty value out of the list. This
+is useful when using account names/login names since only one may be populated:
+
+`{{coalesce .Account.Name .Account.LoginName}}`
+
 ## Tutorial
 
 Refer to the [SSH certificate injection with HCP Boundary](/boundary/tutorials/access-management/hcp-certificate-injection) tutorial to learn how to configure credential injection with SSH certificates using Vault.