Change db_migrator major version on master branch from version 4 to 6

[vaibhavhd]

What I did

DB versions before this change, and the issue of duplicated versions:

201811	version_1_0_1
201911	version_1_0_6
202012	version_2_0_2
202205	version_3_0_7
202211	version_4_0_2
202305	version_4_0_2	<-----	unexpected as major version is reused/duplicated
master	version_4_0_4	<-----	unexpected as major version is reused

New DB versions after making jumps on 202305 and master:

201811	version_1_0_1
201911	version_1_0_6
202012	version_2_0_2
202205	version_3_0_7
202211	version_4_0_2
202305	version_5_0_1	<---- 202305 jumped one version as part of https://github.com/sonic-net/sonic-utilities/pull/2943
master	version_6_0_1	<---- master branch jumps two versions as part of this PR.

How I did it

How to verify it

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)