support mixed app type with appcmds

[kakaZhou719]

Describe what this PR does / why we need it

kubefile:

FROM scratch
APP yamlapp local://yamlcontext
APP shellapp local://shellcontext
APP mixedapp local://install.sh local://mixedcontext
APPCMDS mixedapp ["kubectl apply -f app.yaml"]
LAUNCH ["mixedapp","shellapp"]

├── context
│   ├── app.yaml
│   └── install.sh
├── install.sh
├── Kubefile
├── shellcontext
│   ├── a.sh
│   ├── b.sh
│   └── c.sh
└── yamlcontext
    ├── a.yaml
    ├── b.yaml
    └── c.yaml

if app build context is mixed, need to specify APPCMDS if no app type is detected.

Does this pull request fix one issue?

fixes #1993

Describe how you did it

Describe how to verify it

Special notes for reviews

[codecov-commenter]

Codecov Report

Base: 18.34% // Head: 18.58% // Increases project coverage by +0.23% 🎉

Coverage data is based on head (280bf8c) compared to base (462034d).
Patch coverage: 25.00% of modified lines in pull request are covered.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2028      +/-   ##
==========================================
+ Coverage   18.34%   18.58%   +0.23%     
==========================================
  Files         101      101              
  Lines        9222     9222              
==========================================
+ Hits         1692     1714      +22     
+ Misses       7299     7279      -20     
+ Partials      231      229       -2     

Impacted Files	Coverage Δ
build/kubefile/parser/utils.go	61.00% <9.09%> (+10.68%)	⬆️
build/kubefile/parser/kubefile.go	34.98% <32.00%> (+1.77%)	⬆️

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[starnop]

/test all

[zhy76]

/test run

[zhy76]

/test run

[starnop]

/test run

[starnop]

LGTM