Upgraded LDAP to use 3.4.12

[shoaebjindani]

Upgraded LDAP dependency to v3.4.12
Includes performance and stability improvements
Keeps project aligned with latest upstream fixes

[shoaebjindani]

@bestbeforetoday can you please review and merge ?

[bestbeforetoday]

@shoaebjindani can you explain the intent of this pull request? It appears to only add some additional indirect dependencies that are not actually used by the fabric-ca code. For example, running go mod why github.com/go-ldap/ldap/v3 reports:

main module does not need package github.com/go-ldap/ldap/v3

Running go mod tidy removes all the additions you have made since they are not used.

Is your intent to replace gopkg.in/ldap.v2 with github.com/go-ldap/ldap/v3? If so, you need to modify the code that references it in lib/server/ldap/client.go and update the module dependencies accordingly.