Add LDAP feature CLI support

[davidpil2002]

What I did

Add LDAP CLI

How I did it

created the CLI by using YANG model generator, the YANG model can be found in the LDAP HLD: https://github.com/sonic-net/SONiC/pull/1487

How to verify it

Manually: you can use configurations command like"config ldap global " or "show ldap global" (more examples in the HLD.) Auto: 1.There are unitest of each policy including good & bad flow in this commit, that should pass.

Previous command output (if the output of a command-line utility has changed)

No prev commands - New feature

New command output (if the output of a command-line utility has changed)

sudo show ldap global 
BIND DN                       BIND PASSWORD      BIND TIMEOUT  LDAP VERSION    BASE DN            LDAP PORT      TIMEOUT
----------------------------  ---------------  --------------  --------------  -----------------  -----------  ---------
cn=ldapadm,dc=test1,dc=test2  password            2              3             dc=test1,dc=test2  389                  2

[liat-grozovik]

@lguohan who should review and provide feedback?

[fastiuk]

@madhupalu , please approve if everything looks good

[qiluo-msft]

@madhupalu Do you have more comments?

[davidpil2002]

need to update command reference guide

rebase and update Command-Reference.md file