Add this file both to the main LND directory so that devs can use it for
local linter runs and also add it to the `tools` directory so that the
docker environment used to run the linter in CI has access to it. A
custom linter binary can be built via `golangci-lint custom`. This will
pull in and register all the plugins listed in the new config file when
building the new binary. The new binary can then be run using
`custom-gcl run`.
Bump all build go versions to v1.21.0
Bump the minimum build package version to v1.19.0
Debian "buster" is not longer supported. Security updates have been
discontinued since June 30th 2022. We will build using the latest
version, "bookworm".
As usual, we keep with the last two Go versions, which means the last
year of Go release (they release every 6 months or so).
This change means we can now use the type params (generics) in the
project!
