Revert "rename "pager playbook" to "monitoring warnings" everywhere"

Actually, "monitoring warnings" is less meaningful in some cases.

For example in the case of tls, it talks about emails from Digicert,
which is not per se a monitoring warning. Similarly, the Ganeti
documentation talks about I/O overloads and other conditions that are
not necessarily raised by the monitoring system, but could be raised
by our "human nagioses" (e.g. "humans" saying "this is slow!").

This reverts commit 85d5423f.

tsa/howto/cache.mdwn

@@ -52,7 +52,7 @@ then hit `;` to enter the SQL query mode and issue this query:
 
 See also [[logging]] for more information about lnav.
 
-## Monitoring warnings
+## Pager playbook
 
 The only monitoring for this service is to ensure the proper number of
 nginx processes are running. If this gets triggered, the fix might be

tsa/howto/drbd.mdwn

@@ -65,7 +65,7 @@ Finding which host is associated with this device is easy: just call
 
 It's the host `gettor-01`.
 
-## Monitoring warnings
+## Pager playbook
 
 ### Resyncing disks
 

tsa/howto/fabric.mdwn

@@ -115,7 +115,7 @@ how to write new tasks.
         $ fab -H perdulce.torproject.org host.uptime
          18:06:56 up 24 days, 19:48,  1 user,  load average: 0.00, 0.00, 0.02
 
-## Monitoring warnings
+## Pager playbook
 
 N/A for now. Fabric is an ad-hoc tool and, as such, doesn't have
 monitoring that should trigger a response. It *could* however be used

tsa/howto/ganeti.mdwn

@@ -751,7 +751,7 @@ IP. You can still do so with:
 
     gnt-instance modify --net -1:add,ip=116.202.120.174,network=gnt-fsn test01.torproject.org
 
-## Monitoring warnings
+## Pager playbook
 
 ### I/O overload
 

tsa/howto/prometheus.mdwn

@@ -29,7 +29,7 @@ dashboards for most purposes other than debugging.
 
 # How-to
 
-## Monitoring warnings
+## Pager playbook
 
 TBD.
 

tsa/howto/submission.mdwn

@@ -40,7 +40,7 @@ This document describes the implementation of a **MSA**, although the
 service will most likely also include a **MTA** functionality in that
 it will actually deliver emails to targets.
 
-## Monitoring warnings
+## Pager playbook
 ## Disaster recovery
 
 N/A. The server should be rebuildable from scratch using the Puppet

tsa/howto/template.mdwn

@@ -17,7 +17,7 @@
 
 <!-- more in-depth procedure that may require interpretation -->
 
-## Monitoring warnings
+## Pager playbook
 
 <!-- information about common errors from the monitoring system and -->
 <!-- how to deal with them. this should be easy to follow: think of -->

tsa/howto/tls.mdwn

@@ -127,7 +127,7 @@ Then run Puppet on all affected hosts, for example the static mirrors:
 
     cumin 'C:roles::static_mirror_web' 'puppet agent -t'
 
-## Monitoring warnings
+## Pager playbook
 
  * if you get email from Digicert, ask the Tor Browser team, they use
    it to sign code (see "Design" below for more information about