[YSQL] Rebuild the index using reindex if it gets invalidated

[adil246]

Jira Link: DB-983
Issue
Support index rebuilt using Reindex or Reindex concurrently if the index is in an invalid state due to invalid data, corruption, or failure to build. In the below example, it fails to create an index, marked as invalid, but the index table gets created.

yugabyte=# \d foo;
                           Table "public.foo"
 Column |       Type        | Collation | Nullable |      Default
--------+-------------------+-----------+----------+--------------------
 id     | uuid              |           | not null | uuid_generate_v1()
 b      | character varying |           |          |
Indexes:
    "foo_pkey" PRIMARY KEY, lsm (id HASH)
    "foo_b_idx" UNIQUE, lsm (b HASH) INVALID

yugabyte=# explain analyze select * from foo where b='jsmith';
                                            QUERY PLAN
---------------------------------------------------------------------------------------------------
 Seq Scan on foo  (cost=0.00..102.50 rows=1000 width=48) (actual time=4.376..6.159 rows=1 loops=1)
   Filter: ((b)::text = 'jsmith'::text)
   Rows Removed by Filter: 1
 Planning Time: 0.047 ms
 Execution Time: 6.227 ms
(5 rows)

yugabyte=# reindex index foo_b_idx;
ERROR:  REINDEX not supported yet
LINE 1: reindex index foo_b_idx;
        ^
HINT:  Please report the issue on https://github.com/YugaByte/yugabyte-db/issues
yugabyte=#

yugabyte=# reindex index concurrently foo_b_idx;
ERROR:  syntax error at or near "concurrently"
LINE 1: reindex index concurrently foo_b_idx;

 ./yb-admin --master_addresses 127.0.0.1:7100,127.0.0.2:7100,127.0.03:7100 list_tables include_db_type include_table_id include_table_type |grep -i idx
ysql.yugabyte.foo_b_idx 000030af000030008000000000004014 index