doc: Update PAT prefix

Updates docs around Project Access Token
prefixes to specify the default as `glpat-`

doc/user/project/settings/project_access_tokens.md

@@ -10,6 +10,7 @@ type: reference, howto
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/210181) in GitLab 13.0.
 > - [Became available on GitLab.com](https://gitlab.com/gitlab-org/gitlab/-/issues/235765) in GitLab 13.5 for paid groups only.
 > - [Feature flag removed](https://gitlab.com/gitlab-org/gitlab/-/issues/235765) in GitLab 13.5.
+> - [Changed](https://gitlab.com/gitlab-org/gitlab/-/issues/342327) in GitLab 14.5. Default prefix added.
 
 Project access tokens are similar to [personal access tokens](../../profile/personal_access_tokens.md)
 except they are attached to a project rather than a user. They can be used to:
@@ -32,6 +33,9 @@ Project access tokens:
 For examples of how you can use a project access token to authenticate with the API, see the
 [relevant section from our API Docs](../../../api/index.md#personalproject-access-tokens).
 
+NOTE:
+For GitLab.com and new self-managed instances, the default prefix is `glpat-`.
+
 ## Creating a project access token
 
 1. Log in to GitLab.