Enhancement CBO (#2563)

[ti-chi-bot]

This is an automated cherry-pick of #2563

What problem does this PR solve?

After this PR, TiSpark will choose the store according to the min cost between tikv table scan, tikv index scan and tifalsh scan.

Before this pr, TiSpark only compare tikv table scan and tiflash scan, and usually choose tiflash once the table has tiflash replica.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Daemonxiao
• shiyuhang0

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[shiyuhang0]

/run-all-tests

[shiyuhang0]

/run-all-tests

[shiyuhang0]

/merge

[ti-chi-bot]

@shiyuhang0: /merge in this pull request requires 2 approval(s).

In response to this:

/merge

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[shiyuhang0]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 77d9068