Fix invalid storage dir configurations lead to unexpected behavior (#4105)

[ti-chi-bot]

This is an automated cherry-pick of #4105

What problem does this PR solve?

Issue Number: close #4093

Problem Summary:
If the user set the config file with

[storage]
[storage.main]
dir = "/data0/db"
# Should be: dir = ["/data0/db"]
[storage.raft]
dir = "/data0/db"
# Should be: dir = ["/data0/db"]

If storage.main.dir,storage.latest.dir,storage.raft.dir is a string instead of string-array, TiFlash now considers it is an empty array without any warning/exception, which leads to unexpected behavior

What is changed and how it works?

Check whether storage.main.dir, storage.latest.dir, storage.raft.dir is string array or not. If not, throw an exception and stop tiflash.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Fix the bug that invalid storage dir configurations lead to unexpected behavior

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[JaySon-Huang]

No further planned patch version on release-4.0. Close