[DSL] Allow specifying targets to generate in the DSL

[c-harding]

Revert #399, so the Templefile can specify the targets to generate. This is needed for running a generator on the OpenAPI spec.

[codecov]

Codecov Report

Merging #400 into develop will decrease coverage by 0.02%.
The diff coverage is 94.11%.

@@             Coverage Diff             @@
##           develop     #400      +/-   ##
===========================================
- Coverage    98.95%   98.93%   -0.03%     
===========================================
  Files          137      137              
  Lines         3167     3179      +12     
  Branches        51       44       -7     
===========================================
+ Hits          3134     3145      +11     
- Misses          33       34       +1     

Impacted Files	Coverage Δ
src/main/scala/temple/DSL/syntax/DSLRootItem.scala	100.00% <ø> (ø)
src/main/scala/temple/ast/Metadata.scala	100.00% <ø> (ø)
...in/scala/temple/DSL/semantics/ServiceRenamer.scala	96.29% <66.66%> (-3.71%)	⬇️
src/main/scala/temple/DSL/semantics/Analyzer.scala	100.00% <100.00%> (ø)
...rc/main/scala/temple/DSL/semantics/Validator.scala	100.00% <100.00%> (ø)
src/main/scala/temple/ast/Templefile.scala	100.00% <100.00%> (ø)

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