Support migration data from source with different time_zone by default

[glorv]

What problem does this PR solve?

Automatically adapt source and target DB time_zone settings so users don't need to explicitly set timezone in dm config.

close #1691

What is changed and how it works?

• Deprecated the timezone setting in dm config. (maybe we should directly remove this config field)
• Always set timezone='+00:00' for all db connections in dumpling/loader/syncer.

Check List

Tests

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

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to be included in the release note

[glorv]

/run-all-tests

[glorv]

/run-unit-test

[lance6716]

maybe we should directly remove this config field

we can't remove it because I remember there's a checking about undecoded config items, to fail the user of mistyping. (And I think this also disables smoothly downgrade from a version with more config items)

[lance6716]

we should log a warning if overwrite user's timezone in session variables. rest lgtm

[glorv]

we should log a warning if overwrite user's timezone in session variables. rest lgtm

done

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lance6716
• lichunzhu

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[glorv]

/merge

[ti-chi-bot]

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

Commit hash: a046f1e

[lance6716]

/cherry-pick release-20.

[lance6716]

/cherry-pick release-2.0

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #1714.

[ti-chi-bot]

@lance6716: cannot checkout release-20.: error checking out release-20.: exit status 1. output: error: pathspec 'release-20.' did not match any file(s) known to git

In response to this:

/cherry-pick release-20.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against pingcap/dm#release-2.0 from head ti-chi-bot:cherry-pick-1670-to-release-2.0: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-1670-to-release-2.0."}],"documentation_url":"https://docs.github.com/rest/reference/pulls#create-a-pull-request"}

[ti-chi-bot]

@lance6716: new pull request could not be created: failed to create pull request against pingcap/dm#release-2.0 from head ti-chi-bot:cherry-pick-1670-to-release-2.0: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-1670-to-release-2.0."}],"documentation_url":"https://docs.github.com/rest/reference/pulls#create-a-pull-request"}

In response to this:

/cherry-pick release-2.0

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.