Make sql backend optional

[nazar-pc]

Maybe consider making this feature optional? It pulls way too many dependencies, including OpenSSL.

Originally posted by @nazar-pc in #883 (comment)

[sorpaas]

The goal is actually to completely remove the old backend and switch everyone to sql. Do you have any particular reasons not to use the sql backend?

[nazar-pc]

Hm... not many except it is PITA to deal with OpenSSL when cross-compiling for aarch64 on amd64.

So even though I did not add SQL backend to our service code, it is still pulled in via dependencies, compiled and caused headache that I would rather not have. This is the first and only dependency pulling OpenSSL in our huge monorepo.

[vedhavyas]

This issue was fixed in #1089

[nazar-pc]

Nice, thank you!