Update meltano.yml using new target-snowflake-gitlab variant

Need to do a couple of things:

• Repo https://gitlab.com/gitlab-data/edcast-target-snowflake should be renamed to something like target-snowflake-gitlab to represent our for of the target
• Clean up target-snowflake and use our variant of it (after renaming). Think target name target-snowflake-gitlab is suitable for this purpose.
• Every tap we are using should use a new target target-snowflake-gitlab.
• Update the documentation about which target-snowflake we are using https://gitlab.com/gitlab-data/gitlab-data-meltano/-/blob/main/README.md