pdms: optimize upgrade pdms to avoid unnecessary primary transfer

[HuSharp]

What problem does this PR solve?

What is changed and how it works?

ref tikv/pd#7995

When we have 3 pdms, pdms-0/pdms-1/pdms-2, when pdms-2 is primary

• upgrade pdms-2 firstly maybe transfer primary to pdms-0
• and then uprade pdms-0 will transfer primary again

upgrade pdms primary in last place can avoid  unnecessary primary transfer

Check List

Tests

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

Release notes:

NONE

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