postgresqlreceiver: Add missing units in metadata.yaml (#23571)

Metric unit is required, see:
https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/cmd/mdatagen/metadata-schema.yaml#L72-L73.

This PR adds the unit to metrics where this is missing:
- postgresql.bgwriter.maxwritten
- postgresql.table.count

.chloggen/add-units-postgresqlreceiver.yaml

@@ -0,0 +1,24 @@
+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: postgresqlreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Adds unit to metrics where this was missing.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [23571]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: |
+  Affected metrics can be found below.
+  - postgresql.bgwriter.maxwritten
+  - postgresql.table.count
+

receiver/postgresqlreceiver/documentation.md

@@ -82,7 +82,7 @@ Number of times the background writer stopped a cleaning scan because it had wri
 
 | Unit | Metric Type | Value Type | Aggregation Temporality | Monotonic |
 | ---- | ----------- | ---------- | ----------------------- | --------- |
-|  | Sum | Int | Cumulative | true |
+| 1 | Sum | Int | Cumulative | true |
 
 ### postgresql.blocks_read
 
@@ -226,7 +226,7 @@ Number of user tables in a database.
 
 | Unit | Metric Type | Value Type | Aggregation Temporality | Monotonic |
 | ---- | ----------- | ---------- | ----------------------- | --------- |
-|  | Sum | Int | Cumulative | false |
+| {table} | Sum | Int | Cumulative | false |
 
 ### postgresql.table.size
 

receiver/postgresqlreceiver/metadata.yaml

@@ -126,6 +126,7 @@ metrics:
       aggregation: cumulative
       monotonic: true
       value_type: int
+    unit: 1
   postgresql.blocks_read:
     enabled: true
     description: The number of blocks read.
@@ -235,6 +236,7 @@ metrics:
       aggregation: cumulative
       monotonic: false
       value_type: int
+    unit: "{table}"
   postgresql.table.size:
     attributes: []
     description: Disk space used by a table.