Update docker setup example

[Michal-Leszczynski]

Previously I wasn't able to follow our docker setup example because of two reasons:

• too little memory assigned to SM DB
• incorrect echo behavior when writing config files

Now it should work fine.
Fixes #3672

[Michal-Leszczynski]

@karol-kokoszka Could you take a look and check if fixed example works for you as well?

[karol-kokoszka]

nice catch !

It may be that scylla-university uses same examples to setup manager in docket env.

👍 from my side

[Michal-Leszczynski]

From what I see in example used in Scylla University, it actually doesn't use echo -e and it uses older Scylla version, that should work fine with less memory, so I don't think that there is a need to update that.