Add /configure_telemetry API endpoint (#11117)

Work on https://github.com/neondatabase/cloud/issues/23721 and
https://github.com/neondatabase/cloud/issues/23714

Depends on https://github.com/neondatabase/neon/pull/11111

- Add `/configure_telemetry` API endpoint
- Support second rsyslog configuration for Postgres logs export
- Enable logs export when compute feature is enabled and configure
Postgres to send logs to syslog

I have used `/configure_telemetry` name because in the future I see it
also being used for configuring a `pg_tracing` extension to export
traces. Let me know if you'd rather have these APIs separate. In this
case we can rename it to `/configure_rsyslog`.

compute/vm-image-spec-bookworm.yaml

@@ -39,6 +39,13 @@ commands:
     user: nobody
     sysvInitAction: respawn
     shell: '/bin/sql_exporter -config.file=/etc/sql_exporter_autoscaling.yml -web.listen-address=:9499'
+  # Rsyslog by default creates a unix socket under /dev/log . That's where Postgres sends logs also.
+  # We run syslog with postgres user so it can't create /dev/log. Instead we configure rsyslog to
+  # use a different path for the socket. The symlink actually points to our custom path.
+  - name: rsyslogd-socket-symlink
+    user: root
+    sysvInitAction: sysinit
+    shell: "ln -s /var/db/postgres/rsyslogpipe /dev/log"
   - name: rsyslogd
     user: postgres
     sysvInitAction: respawn
@@ -77,6 +84,9 @@ files:
 # compute_ctl will rewrite this file with the actual configuration, if needed.
   - filename: compute_rsyslog.conf
     content: |
+      # Syslock.Name specifies a non-default pipe location that is writeable for the postgres user.
+      module(load="imuxsock" SysSock.Name="/var/db/postgres/rsyslogpipe") # provides support for local system logging
+
       *.*    /dev/null
       $IncludeConfig /etc/rsyslog.d/*.conf
 build: |

compute/vm-image-spec-bullseye.yaml

@@ -39,6 +39,13 @@ commands:
     user: nobody
     sysvInitAction: respawn
     shell: '/bin/sql_exporter -config.file=/etc/sql_exporter_autoscaling.yml -web.listen-address=:9499'
+  # Rsyslog by default creates a unix socket under /dev/log . That's where Postgres sends logs also.
+  # We run syslog with postgres user so it can't create /dev/log. Instead we configure rsyslog to
+  # use a different path for the socket. The symlink actually points to our custom path.
+  - name: rsyslogd-socket-symlink
+    user: root
+    sysvInitAction: sysinit
+    shell: "ln -s /var/db/postgres/rsyslogpipe /dev/log"
   - name: rsyslogd
     user: postgres
     sysvInitAction: respawn
@@ -77,6 +84,9 @@ files:
 # compute_ctl will rewrite this file with the actual configuration, if needed.
   - filename: compute_rsyslog.conf
     content: |
+      # Syslock.Name specifies a non-default pipe location that is writeable for the postgres user.
+      module(load="imuxsock" SysSock.Name="/var/db/postgres/rsyslogpipe") # provides support for local system logging
+
       *.*    /dev/null
       $IncludeConfig /etc/rsyslog.d/*.conf
 build: |