Escape commas in __P(basedn) default to fix JMeter plan compile

The benchmark plan failed to compile with "__P called with wrong number of
parameters. Actual: 3. Expected: >= 1 and <= 2": the default value in
${__P(basedn,dc=example,dc=com)} contains commas, which JMeter's function
parser treats as extra argument separators. Escape them as
${__P(basedn,dc=example\,dc=com)} in the ADMIN_CONNECT and BIND samplers.

Without this the tree never compiled, so no statistics.json was produced and
the summary step failed on jq. Verified locally with JMeter 5.6.3: the plan
now compiles and runs, and report generation produces statistics.json.