drop sharded table if exists test

[donhardman]

No description provided.

[donhardman]

Implemented: #448

[donhardman]

Let's add tests for these cases:

1. Create a sharded table 'a'
2. Use DROP SHARDED TABLE a with IF EXISTS and verify it works
3. Use DROP SHARDED TABLE a with IF EXISTS on a non-existent table
4. Use DROP SHARDED TABLE a with IF EXISTS on a regular RT table

[PavelShilin89]

@donhardman This issue blocked manticoresoftware/manticoresearch#2963

[donhardman]

Unblocked

[PavelShilin89]

@donhardman In this PR - manticoresoftware/manticoresearch#3012, a Clt-test has been created with the new logic in mind. Please give feedback or approval to merge.

[donhardman]

Let's add same test for clustered environment