mk_core: mk_rconf: Be more verbose on indentation errors (#322)
mk_core: mk_rconf: Be more verbose on indentation errors (#322)

This extends the verification logic for indentation, so that
users can distinguish the following three failure modes.

    [INPUT]
      Name dummy
     Tag 1

    => (1) Indentation level is too low

    [INPUT]
        Name dummy
    \tTag 1

    => (2) Inconsitent use of tab and space

    [INPUT]
      Name dummy
       Tag 1

    => (3) Extra indentation level found

Especially (2) was somewhat difficult for users to recognize what
is wrong, because a) indentation looks fine on text editor, b) but
Fluent Bit is still complaining.

Signed-off-by: Fujimoto Seiji <ef879192bb1e41d519c82cf76440dc8e9a530806@clear-code.com>
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