Add restrictions while setting search field attribute

[sazzad16]

• Attribute cannot be null
• Attribute cannot be set multiple times

[codecov-commenter]

Codecov Report

Merging #3124 (c4aff05) into master (e41904e) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #3124      +/-   ##
============================================
- Coverage     66.69%   66.68%   -0.01%     
- Complexity     4234     4236       +2     
============================================
  Files           219      219              
  Lines         13757    13761       +4     
  Branches        799      800       +1     
============================================
+ Hits           9175     9177       +2     
- Misses         4248     4250       +2     
  Partials        334      334              

Impacted Files	Coverage Δ
...ain/java/redis/clients/jedis/search/FieldName.java	65.11% <100.00%> (+3.57%)	⬆️
...in/java/redis/clients/jedis/ConnectionFactory.java	63.26% <0.00%> (-4.09%)	⬇️

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