*: unify terms

[ran-huang]

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

• on-premises -> self-hosted
• 私有部署 -> 自托管

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

• [x] master (the latest development version)
• [x] v1.5 (TiDB Operator 1.5 versions)
• [x] v1.4 (TiDB Operator 1.4 versions)
• [x] v1.3 (TiDB Operator 1.3 versions)
• [x] v1.2 (TiDB Operator 1.2 versions)

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

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

[ti-chi-bot[bot]]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• qiancai

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[ran-huang]

/merge

[ti-chi-bot[bot]]

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

Commit hash: 069027e09968d9c4c5ba4df571a70e272b723c79

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-1.5: #2373.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-1.2: #2374.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-1.3: #2375.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-1.4: #2376.