sync-diff-inspector: support base64 encoded password

[lichunzhu]

What problem does this PR solve?

Issue Number: close https://github.com/pingcap/tidb-tools/issues/687

What is changed and how it works?

support base64 encoded password like lightning did in https://github.com/pingcap/tidb/pull/31195

Check List

Tests

• Unit test

Code changes

• Has exported function/method change

Side effects

• None

Related changes

• Need to update the documentation
• Need to be included in the release note

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Leavrth

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[lichunzhu]

/merge

[ti-chi-bot]

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

Commit hash: 4f18250e1e2eb6b65015897b0a87791ee1976202