Use LMDB as DB-less storage

[dndx]

DO NOT use in prod, PoC only. It also nukes the shdict based DB-less storage completely from orbit.

[fairyqb]

when data storage support ETCD, REDIS,based on the existing infrastructure, reduce management and maintenance costs ,thanks
@bungle @Tieske @kikito @gszr

[bungle]

when data storage support ETCD, REDIS,based on the existing infrastructure, reduce management and maintenance costs

I hear you, but the LMDB as proposed here is about improving our current dbless, with an in-process database lmdb. The goal is to improve hybrid and dbless modes. Things like incremental/differential updates, two-way communication between CP & DP, and possible between DPs. The lmdb here is replacing Nginx shared memory zones used currently with dbless and hybrid data plane nodes. As far as I know, we don't currently plan adding etcd or redis support for configuration data. But redis could still be more tightly integrated for example for distributed caching.

[dndx]

Superseded by #8224.