bump operator to v1.4.0 for release-1.4

[csuzhangxc]

First-time contributors' checklist

• I've signed Contributor License Agreement that's required for repo owners to accept my contribution.

What is changed, added, or deleted? (Required)

find . -type f | xargs sed -i "s/tidb-operator\/master/tidb-operator\/v1.4.0/g"
find . -type f | xargs sed -i "s/v1.4.0-beta.3/v1.4.0/g"

Which TiDB Operator version(s) do your changes apply to? (Required)

• master (the latest development version)
• v1.4 (TiDB Operator 1.4 versions)
• v1.3 (TiDB Operator 1.3 versions)
• v1.2 (TiDB Operator 1.2 versions)
• v1.1 (TiDB Operator 1.1 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):

[ti-chi-bot]

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• ran-huang

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[ran-huang]

/merge

[ti-chi-bot]

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

Commit hash: 136c65e