Fix TidbDashboard baseImage parsing fault (#5014)

[ti-chi-bot]

This is an automated cherry-pick of #5014

Fix wrong baseImage version adapt for image tag while the repo has specified a unique port with ':'.

What problem does this PR solve?

Fix the bug that baseImage auto version adapt can be executed unexpected while the repo has specified a unique port with ':'.

e.g.
If baseImage = example.registry.com:30000/foo/pingcap/tidb-dashboard:vx.y.z, the final image will be "example.registry.com:vx.y.z".

What is changed and how does it work?

Judge whether there were '' after the last ':'. If there is one, it is not a ':' for the image tag.

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

Fix TidbDashboard baseImage parsing fault.

[ti-chi-bot]

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