cluster: fix tiproxy config and version

[xhebox]

What problem does this PR solve?

1, require-backend-tls is useless
2. now we use nightly version by default
3. fix a bug where configs are lost

Check List

Tests

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

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

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

Release notes:

NONE

[kaaaaaaang]

I do not think it is a good idea to use nightly by default in tiup-cluster. For example，user may use tiup-cluster v1.14.1 years later.

[xhebox]

I do not think it is a good idea to use nightly by default in tiup-cluster. For example，user may use tiup-cluster v1.14.1 years later.

Addressed. Fallback to "" by default. Or "nightly", if either component version or cluster version is.

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (1210bc2) 55.53% compared to head (baa7cac) 55.31%.

❗ Current head baa7cac differs from pull request most recent head 0470547. Consider uploading reports for the commit 0470547 to get more accurate results

Files	Patch %	Lines
pkg/cluster/spec/tiproxy.go	50.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2354      +/-   ##
==========================================
- Coverage   55.53%   55.31%   -0.22%     
==========================================
  Files         329      329              
  Lines       34836    34841       +5     
==========================================
- Hits        19344    19270      -74     
- Misses      13179    13258      +79     
  Partials     2313     2313              

Flag	Coverage Δ
cluster	44.63% <50.00%> (-0.25%)	⬇️
dm	25.45% <0.00%> (-0.04%)	⬇️
playground	15.36% <0.00%> (-0.01%)	⬇️
tiup	33.59% <ø> (ø)
unittest	22.34% <0.00%> (-<0.01%)	⬇️

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[kaaaaaaang]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-01-09 06:24:47.467723656 +0000 UTC m=+338077.051977328: ☑️ agreed by kaaaaaaang.

[kaaaaaaang]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kaaaaaaang

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