Build documentation for the new added metrics

docs/user/collected-metrics/metrics.md

@@ -129,7 +129,9 @@ The following metrics are added to the ping:
 | Name | Type | Description | Data reviews | Extras | Expiration | [Data Sensitivity](https://wiki.mozilla.org/Firefox/Data_Collection) |
 | --- | --- | --- | --- | --- | --- | --- |
 | glean.error.preinit_tasks_overflow |[counter](https://mozilla.github.io/glean/book/user/metrics/counter.html) |The number of tasks queued in the pre-initialization buffer. Only sent if the buffer overflows.  |[1](https://bugzilla.mozilla.org/show_bug.cgi?id=1609482#c3)||never |1 |
+| glean.upload.deleted_pings_after_quota_hit |[counter](https://mozilla.github.io/glean/book/user/metrics/counter.html) |The number of pings deleted after the quota for the size of the pending pings directory is hit. Since quota is only calculated for the pending pings directory, and deletion request ping live in a different directory, deletion request pings are never deleted.  |[1](https://bugzilla.mozilla.org/show_bug.cgi?id=1601550#c3)||never |1 |
 | glean.upload.discarded_exceeding_pings_size |[memory_distribution](https://mozilla.github.io/glean/book/user/metrics/memory_distribution.html) |The size of pings that exceeded the maximum ping size allowed for upload.  |[1](https://bugzilla.mozilla.org/show_bug.cgi?id=1597761#c10)||never |1 |
+| glean.upload.pending_pings_directory_size |[memory_distribution](https://mozilla.github.io/glean/book/user/metrics/memory_distribution.html) |The size of the pending pings directory upon initialization of Glean. This does not include the size of the deletion request pings directory.  |[1](https://bugzilla.mozilla.org/show_bug.cgi?id=1601550#c3)||never |1 |
 | glean.upload.ping_upload_failure |[labeled_counter](https://mozilla.github.io/glean/book/user/metrics/labeled_counters.html) |Counts the number of ping upload failures, by type of failure. This includes failures for all ping types, though the counts appear in the next successfully sent `metrics` ping.  |[1](https://bugzilla.mozilla.org/show_bug.cgi?id=1589124#c1)|<ul><li>status_code_4xx</li><li>status_code_5xx</li><li>status_code_unknown</li><li>unrecoverable</li><li>recoverable</li></ul>|never |1 |