fix #3551 and optimize ldap samples

[nobodyiam]

What's the purpose of this PR

Fix the issue that apollo portal won't start when ldap is enabled and optimize ldap samples.

Which issue(s) this PR fixes:

Fixes #3551

Brief changelog

1. Exclude LdapAutoConfiguration
2. Simplify ldap configuration samples

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• Read the Contributing Guide before making this pull request.
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[codecov-io]

Codecov Report

Merging #3561 (4f4f20d) into master (8285504) will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #3561      +/-   ##
============================================
+ Coverage     50.93%   50.95%   +0.02%     
- Complexity     2322     2324       +2     
============================================
  Files           447      447              
  Lines         13989    13989              
  Branches       1423     1423              
============================================
+ Hits           7125     7128       +3     
+ Misses         6374     6373       -1     
+ Partials        490      488       -2     

Impacted Files	Coverage Δ	Complexity Δ
...rip/framework/apollo/portal/PortalApplication.java	33.33% <ø> (ø)	1.00 <0.00> (ø)
.../framework/apollo/spring/property/SpringValue.java	89.47% <0.00%> (+1.75%)	21.00% <0.00%> (+1.00%)
...rk/apollo/spring/property/SpringValueRegistry.java	88.88% <0.00%> (+5.55%)	11.00% <0.00%> (+1.00%)

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