manager/deploy: do not allow deploying of empty topology

[AstroProfundis]

What problem does this PR solve?

Fix #783

Check List

Tests

• Manual test (add detailed scripts or steps below)
  

Code changes

• Has exported function/method change

Related changes

• Need to cherry-pick to the release branch

Release notes:

fix: not allowing empty topology file for deploy

[codecov-io]

Codecov Report

Merging #994 (9019f26) into master (87f670b) will increase coverage by 0.01%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master     #994      +/-   ##
==========================================
+ Coverage   55.55%   55.56%   +0.01%     
==========================================
  Files         279      279              
  Lines       19719    19727       +8     
==========================================
+ Hits        10954    10962       +8     
  Misses       7054     7054              
  Partials     1711     1711              

Flag	Coverage Δ
cluster	43.46% <75.00%> (+0.02%)	⬆️
dm	23.87% <75.00%> (+0.02%)	⬆️
integrate	49.83% <75.00%> (+0.02%)	⬆️
playground	20.28% <ø> (ø)
tiup	16.46% <ø> (ø)
unittest	23.03% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/cluster/manager/deploy.go	70.35% <75.00%> (+0.19%)	⬆️
pkg/cluster/api/pdapi.go	61.30% <0.00%> (+0.61%)	⬆️

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[lucklove]

/lgtm

[lucklove]

/merge

[ti-chi-bot]

Can merge label has been added.

Git tree hash: 9019f26

[ti-chi-bot]

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