Document that logger now encodes table arguments in JSON

Related dev. issue(s): https://github.com/tarantool/tarantool/issues/8611
Product: Tarantool
Since: 3.4
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_lua/log/#overview
SME: @ locker

Details

Scope:

• Add info and examples to:
  • https://www.tarantool.io/en/doc/latest/reference/reference_lua/log/#lua-function.log.error
  • https://www.tarantool.io/en/doc/latest/reference/reference_lua/log/#lua-function.log.warn
  • https://www.tarantool.io/en/doc/latest/reference/reference_lua/log/#lua-function.log.info

How it used to work:

tarantool> require('log').info('%s', {foo = 'bar'})
table: 0x41f9d2e8

How it works now:

tarantool> require('log').info('%s', {foo = 'bar'})
{"foo":"bar"}

Note, JSON encoding is enabled only for tables that don't have
the __tostring meta-method:

tarantool> require('log').info('%s', setmetatable({foo = 'bar'}, {__tostring = function() return 'foobar' end}))
foobar

Requested by @ locker in https://github.com/tarantool/tarantool/commit/3db73c65f29a7d1991f7a94e5b488cd7c142bba1.

Start with the root log reference and the three named anchors for log.error, log.warn, and log.info. Add the documented table-argument JSON behavior, the existing examples, and the __tostring exception; done means all three sections describe the output shown in the issue.