remove extra space for string value for postgresql datasource

[Nicole00]

For Postgresql datasource, if source value's data type is CHAR(10) but the value length is less than 10, then data read by spark will be fill with spaces.
Example: data in postgres is "tom" and it's data type is CHAR(10), then after importing, the data in nebula will be "tom ", which is wrong. So we need to remove the extra spaces.

[Nicole00]

This pr has been tested for client import mode and sst import mode for spark2.2, spark2.4 and spark3.0
postgresql:

create table exchange(id INT PRIMARY KEY, col1 CHAR(10), col2 CHAR(10), col3 CHAR(10), col4 CHAR(20), col5 CHAR(30), col6 CHAR(30), col7 CHAR(10));
insert into exchange values (2, 'jina', 'jina', '1000', '2021-12-12', '342786543', 'true', '1.2');

nebula:

create tag player(col1 string, col2 fixed_string(20), col3 int32, col4 date, col5 timestamp, col6 bool, col7 double);
create edge friend(col1 string, col2 fixed_string(20), col3 int32, col4 date, col5 timestamp, col6 bool, col7 double);

[codecov-commenter]

Codecov Report

Merging #65 (242d559) into master (f69bb65) will not change coverage.
The diff coverage is 84.00%.

@@            Coverage Diff            @@
##             master      #65   +/-   ##
=========================================
  Coverage     55.14%   55.14%           
  Complexity       76       76           
=========================================
  Files            17       17           
  Lines          1342     1342           
  Branches        254      254           
=========================================
  Hits            740      740           
  Misses          473      473           
  Partials        129      129           

Impacted Files	Coverage Δ
...m/vesoft/exchange/common/processor/Processor.scala	66.41% <84.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f69bb65...242d559. Read the comment docs.