relay/streamer: move binlog log reader into relay

[D3Hunter]

What problem does this PR solve?

it's first part of subtask 4 in #2214

no code logic change in this pr, to make review/merge easier

What is changed and how it works?

• move binlog log reader into relay
• flat small sub packages
• rename some structs to avoid conflict

Check List

no code logic change

[ti-chi-bot]

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[ti-chi-bot]

@D3Hunter: PR needs rebase.

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[D3Hunter]

closed, move to ticdc