feat: optimize replication information retrieval scope for improved performance

[wadahiro]

Currently, sub scope was used for replication information, which fetched all entries under the base DN. I changed it to base to retrieve information only from the base DN itself. This change improves performance by limiting the scope of the query.

In my case, it took 0m0.069s for the search using sub scope.

$ time ldapsearch -x -h ldap.example.com -D "cn=manager,dc=example,dc=com" -W -b "dc=example,dc=com" -s sub  "contextCSN=*" contextCSN
# extended LDIF
#
# LDAPv3
# base <dc=example,dc=com> with scope baseObject
# filter: contextCSN=*
# requesting: contextCSN
#

# example.com
dn: dc=example,dc=com,
contextCSN: 20241227004734.408350Z#000000#000#000000

# search result
search: 2
result: 0 Success

# numResponses: 2
# numEntries: 1

real    0m0.069s
user    0m0.005s
sys     0m0.000s

It took 0m0.006s for the search using base scope.

$ time ldapsearch -x -h ldap.example.com -D "cn=manager,dc=example,dc=com" -W -b "dc=example,dc=com" -s base  "contextCSN=*" contextCSN
# extended LDIF
#
# LDAPv3
# base <dc=example,dc=com> with scope baseObject
# filter: contextCSN=*
# requesting: contextCSN
#

# example.com
dn: dc=example,dc=com,
contextCSN: 20241227004734.408350Z#000000#000#000000

# search result
search: 2
result: 0 Success

# numResponses: 2
# numEntries: 1

real    0m0.006s
user    0m0.005s
sys     0m0.000s

[fritterhoff]

LGTM. We never noticed this bug since we limited the access for our monitoring user to the base entity only.