Find and replace all nolint instances refering to the `lll` linter and
replace with `ll` which is the name of our custom version of the `lll`
linter which can be used to ignore log lines during linting.
The next commit will do the configuration of the custom linter and
disable the default one.
In this commit, a `DefaultWatchtowerCfg` function is added which is used
to construct a default `lncfg.Watchtower` struct. This is then used to
populate the default watchtower config in the main LND config struct.
