[fix](Nereids) Add alias name for system variable

[keanji-x]

Proposed changes

Issue Number: close #xxx

Add alias name for system variable to fix the col name is the values of system variable like:

mysql> select @@character_set_client;
+--------+
| 'utf8' |
+--------+
| utf8   |
+--------+
==================================
mysql> select @@character_set_client;
+------------------------+
| @@character_set_client |
+------------------------+
| utf8                   |
+------------------------+

Further comments

If this is a relatively large or complex change, kick off the discussion at dev@doris.apache.org by explaining why you chose the solution you did and what alternatives you considered, etc...

[hello-stephen]

(From new machine)TeamCity pipeline, clickbench performance test result:
the sum of best hot time: 55.72 seconds
stream load tsv: 507 seconds loaded 74807831229 Bytes, about 140 MB/s
stream load json: 19 seconds loaded 2358488459 Bytes, about 118 MB/s
stream load orc: 64 seconds loaded 1101869774 Bytes, about 16 MB/s
stream load parquet: 30 seconds loaded 861443392 Bytes, about 27 MB/s
insert into select: 89.4 seconds inserted 10000000 Rows, about 111K ops/s
storage size: 17170114433 Bytes
https://doris-community-test-1308700295.cos.ap-hongkong.myqcloud.com/tmp/20230707154247_clickbench_pr_174300.html

[keanji-x]

run buildall

[hello-stephen]

TeamCity pipeline, clickbench performance test result:
the sum of best hot time: 51.04 seconds
stream load tsv: 447 seconds loaded 74807831229 Bytes, about 159 MB/s
stream load json: 20 seconds loaded 2358488459 Bytes, about 112 MB/s
stream load orc: 57 seconds loaded 1101869774 Bytes, about 18 MB/s
stream load parquet: 28 seconds loaded 861443392 Bytes, about 29 MB/s
insert into select: 67.4 seconds inserted 10000000 Rows, about 148K ops/s
https://doris-community-test-1308700295.cos.ap-hongkong.myqcloud.com/tmp/20230707081209_clickbench_pr_174326.html

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.

[morningman]

LGTM