Update pwd_policy table docs (#33181)

for #31346 

# Details

Updated the docs for the `days_to_expiration` column of the `pwd_policy`
table.

# Checklist for submitter

- [X] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.

changes/31346-update-pww-policy-table-docs

@@ -0,0 +1 @@
+- Updated docs for the `pwd_policy` table to better reflect the meaning of `days_to_expiration`.

schema/osquery_fleet_schema.json

@@ -23352,7 +23352,7 @@
         "name": "days_to_expiration",
         "type": "integer",
         "required": false,
-        "description": "How many days are left for the expiration of the current password."
+        "description": "Synonym for expires_every_n_days (not typically set in macOS 10.15+)."
       },
       {
         "name": "history_depth",

schema/tables/pwd_policy.yml

@@ -17,7 +17,7 @@ columns:
     type: integer
     required: false
     description: |-
-      How many days are left for the expiration of the current password.
+      Synonym for expires_every_n_days (not typically set in macOS 10.15+).
   - name: history_depth
     type: integer
     required: false