asim: add skip_under_ci for some tests in pkg/kv/kvserver/asim/tests

This commit adds the skip_under_ci flag to the `example_rebalancing`,
`example_fulldisk`, `example_liveness`, `example_splitting`, and `example_zone_config`
test files, as they tend to run for a longer duration. We plan to extend this
flag to additional long-running tests in the future.

Epic: none
Release note: none

Author: wenyihu6

pkg/kv/kvserver/asim/tests/testdata/non_rand/example_fulldisk.txt

@@ -1,3 +1,6 @@
+skip_under_ci
+----
+
 # Set every store's capacity to 512 GiB, we will later adjust just one store to
 # have less free capacity.
 gen_cluster nodes=5 store_byte_capacity=549755813888

pkg/kv/kvserver/asim/tests/testdata/non_rand/example_liveness.txt

@@ -1,3 +1,6 @@
+skip_under_ci
+----
+
 # This example sets n7 to dead initially and n5 to decommissioning after 2
 # minutes. The output of replicas per store is then plotted.
 #

pkg/kv/kvserver/asim/tests/testdata/non_rand/example_rebalancing.txt

@@ -1,3 +1,6 @@
+skip_under_ci
+----
+
 # Walk through the basics of the datadriven syntax. Create a state generator
 # where there are 7 stores, 7 ranges and initially the replicas are placed
 # following a skewed distribution (where s1 has the most replicas, s2 has half

pkg/kv/kvserver/asim/tests/testdata/non_rand/example_splitting.txt

@@ -1,3 +1,6 @@
+skip_under_ci
+----
+
 # Explore how load based and sized based splitting occur in isolation. In this
 # example, there is only one store so no rebalancing activity should occur. 
 gen_cluster nodes=1

pkg/kv/kvserver/asim/tests/testdata/non_rand/example_zone_config.txt

@@ -1,3 +1,6 @@
+skip_under_ci
+----
+
 # This test applies a configuration that prioritizes zone constraints, favoring
 # the US_East region. As a result, we expect a majority of replicas to be
 # distributed across stores numbered 1-12, all within the US_East region. The