Add xpack/basic scope to SLM documentation (#51711)

This adds the required

```
[role="xpack"]
[testenv="basic"]
```

To the top of the SLM documentation

Relates to #51678

docs/reference/slm/apis/slm-delete.asciidoc

@@ -1,3 +1,5 @@
+[role="xpack"]
+[testenv="basic"]
 [[slm-api-delete-policy]]
 === Delete snapshot lifecycle policy API
 ++++
@@ -64,4 +66,4 @@ PUT /_slm/policy/daily-snapshots
 --------------------------------------------------
 DELETE /_slm/policy/daily-snapshots
 --------------------------------------------------
-// TEST[continued]
+// TEST[continued]

docs/reference/slm/apis/slm-execute-retention.asciidoc

@@ -1,3 +1,5 @@
+[role="xpack"]
+[testenv="basic"]
 [[slm-api-execute-retention]]
 === Execute snapshot retention policy API
 ++++
@@ -34,4 +36,4 @@ To force removal of expired snapshots:
 POST /_slm/_execute_retention
 --------------------------------------------------
 
-Retention runs asynchronously in the background.
+Retention runs asynchronously in the background.

docs/reference/slm/apis/slm-execute.asciidoc

@@ -1,3 +1,5 @@
+[role="xpack"]
+[testenv="basic"]
 [[slm-api-execute-lifecycle]]
 === Execute snapshot lifecycle policy API
 ++++
@@ -58,4 +60,4 @@ If successful, this request returns the generated snapshot name:
 The snapshot is taken in the background. 
 You can use the<<modules-snapshots,snapshot APIs>> to monitor the status of the snapshot.
 
-To see the status of a policy's most recent snapshot, you can use the <<slm-api-get-policy>>.
+To see the status of a policy's most recent snapshot, you can use the <<slm-api-get-policy>>.

docs/reference/slm/apis/slm-get-status.asciidoc

@@ -1,3 +1,5 @@
+[role="xpack"]
+[testenv="basic"]
 [[slm-api-get-status]]
 === Get {slm} status API
 
@@ -50,4 +52,4 @@ The API returns the following result:
   "operation_mode": "RUNNING"
 }
 --------------------------------------------------
-// TESTRESPONSE[s/"operation_mode": "RUNNING"/"operation_mode": $body.operation_mode/]
+// TESTRESPONSE[s/"operation_mode": "RUNNING"/"operation_mode": $body.operation_mode/]

docs/reference/slm/apis/slm-get.asciidoc

@@ -1,3 +1,5 @@
+[role="xpack"]
+[testenv="basic"]
 [[slm-api-get-policy]]
 === Get snapshot lifecycle policy API
 ++++
@@ -121,4 +123,4 @@ This request returns the following response:
 --------------------------------------------------
 GET /_slm/policy
 --------------------------------------------------
-// TEST[continued]
+// TEST[continued]

docs/reference/slm/apis/slm-put.asciidoc

@@ -1,3 +1,5 @@
+[role="xpack"]
+[testenv="basic"]
 [[slm-api-put-policy]]
 === Put snapshot lifecycle policy API
 ++++
@@ -174,4 +176,4 @@ PUT /_slm/policy/daily-snapshots
 <6> Optional retention configuration
 <7> Keep snapshots for 30 days
 <8> Always keep at least 5 successful snapshots, even if they're more than 30 days old
-<9> Keep no more than 50 successful snapshots, even if they're less than 30 days old
+<9> Keep no more than 50 successful snapshots, even if they're less than 30 days old

docs/reference/slm/apis/slm-start.asciidoc

@@ -1,3 +1,5 @@
+[role="xpack"]
+[testenv="basic"]
 [[slm-api-start]]
 === Start {slm} API
 
@@ -48,4 +50,4 @@ If successful, this request returns:
 {
   "acknowledged": true
 }
---------------------------------------------------
+--------------------------------------------------

docs/reference/slm/apis/slm-stats.asciidoc

@@ -1,3 +1,5 @@
+[role="xpack"]
+[testenv="basic"]
 [[slm-api-get-stats]]
 === Get snapshot lifecycle stats API
 ++++
@@ -43,4 +45,4 @@ The API returns the following response:
   "total_snapshot_deletion_failures": 0
 }
 --------------------------------------------------
-// TESTRESPONSE[s/runs": 13/runs": $body.retention_runs/ s/_failed": 0/_failed": $body.retention_failed/ s/_timed_out": 0/_timed_out": $body.retention_timed_out/ s/"1.4s"/$body.retention_deletion_time/ s/1404/$body.retention_deletion_time_millis/ s/total_snapshots_taken": 1/total_snapshots_taken": $body.total_snapshots_taken/ s/total_snapshots_failed": 1/total_snapshots_failed": $body.total_snapshots_failed/ s/"policy_stats": [.*]/"policy_stats": $body.policy_stats/]
+// TESTRESPONSE[s/runs": 13/runs": $body.retention_runs/ s/_failed": 0/_failed": $body.retention_failed/ s/_timed_out": 0/_timed_out": $body.retention_timed_out/ s/"1.4s"/$body.retention_deletion_time/ s/1404/$body.retention_deletion_time_millis/ s/total_snapshots_taken": 1/total_snapshots_taken": $body.total_snapshots_taken/ s/total_snapshots_failed": 1/total_snapshots_failed": $body.total_snapshots_failed/ s/"policy_stats": [.*]/"policy_stats": $body.policy_stats/]

docs/reference/slm/apis/slm-stop.asciidoc

@@ -1,3 +1,5 @@
+[role="xpack"]
+[testenv="basic"]
 [[slm-api-stop]]
 === Stop {slm} API
 
@@ -45,4 +47,4 @@ include::{docdir}/rest-api/common-parms.asciidoc[tag=timeoutparms]
 [source,console]
 --------------------------------------------------
 POST _slm/stop
---------------------------------------------------
+--------------------------------------------------