refactor: do not log overriding structs

[zmstone]

background

In PR #219 the value wrapper for env override metadata is moved to richmap meta data,
as a result, the wrapping struct's meta data is propagated down to the primitive fields.
but one thing was forgotten (not released yet): the override logging started to repeating the same info at different levels.

change

This PR mutes the struct level logging (because it lacks of sensitive information at wrapping object level)
and only log primitive values instead.

example

before this change:

authentication.1 = EMQX_AUTHENTICATION__1 = #{<<“backend”>> => <<“mysql”>>,<<“database”>> => <<“emqx”>>,<<“enable”>> => true,<<“mechanism”>> => <<“password_based”>>,<<“password”>> => <<“emqx”>>,<<“password_hash_algorithm”>> => #{<<“name”>> => <<“sha256">>,<<“salt_position”>> => <<“prefix”>>},<<“query”>> => <<“SELECT password_hash, salt, is_superuser FROM mqtt_us
er WHERE username = ${username} LIMIT 1">>,<<“server”>> => <<“localhost:3306">>,<<“username”>> => <<“emqx”>>}
authentication.1.password = EMQX_AUTHENTICATION__1 = ******
authentication.1.username = EMQX_AUTHENTICATION__1 = emqx
authentication.1.database = EMQX_AUTHENTICATION__1 = emqx
authentication.1.server = EMQX_AUTHENTICATION__1 = localhost:3306
authentication.1.enable = EMQX_AUTHENTICATION__1 = true
authentication.1.query = EMQX_AUTHENTICATION__1 = SELECT password_hash, salt, is_superuser FROM mqtt_user WHERE username = ${username} LIMIT 1
authentication.1.password_hash_algorithm = EMQX_AUTHENTICATION__1 = #{<<“name”>> => <<“sha256">>,<<“salt_position”>> => <<“prefix”>>}
authentication.1.password_hash_algorithm.salt_position = EMQX_AUTHENTICATION__1 = prefix
authentication.1.password_hash_algorithm.name = EMQX_AUTHENTICATION__1 = sha256
authentication.1.backend = EMQX_AUTHENTICATION__1 = mysql
authentication.1.mechanism = EMQX_AUTHENTICATION__1 = password_based

after this change:

EMQX_AUTHENTICATION__1 [authentication.1]: {...}
EMQX_AUTHENTICATION__1 [authentication.1.password]: ******
EMQX_AUTHENTICATION__1 [authentication.1.username]: emqx
EMQX_AUTHENTICATION__1 [authentication.1.database]: emqx
EMQX_AUTHENTICATION__1 [authentication.1.server]: localhost:3306
EMQX_AUTHENTICATION__1 [authentication.1.enable]: true
EMQX_AUTHENTICATION__1 [authentication.1.query]: SELECT password_hash, salt, is_superuser FROM mqtt_user WHERE username = ${username} LIMIT 1
EMQX_AUTHENTICATION__1 [authentication.1.password_hash_algorithm]: {...}
EMQX_AUTHENTICATION__1 [authentication.1.password_hash_algorithm.salt_position]: prefix
EMQX_AUTHENTICATION__1 [authentication.1.password_hash_algorithm.name]: sha256
EMQX_AUTHENTICATION__1 [authentication.1.backend]: mysql
EMQX_AUTHENTICATION__1 [authentication.1.mechanism]: password_based