[Playground][Backend][Bug]: Moving the initialization of properties file

[vchunikhin]

fixes #22309

@VladMatyunin

Since Sdk_SDK_UNSPECIFIED in charge of datastore interaction, the properties file is needed only for this sdk
Otherwise, will be the next error for other SDKs like that:

│panic: Config File "properties" Not Found in "[/]"
│
│goroutine 1 [running]:
│main.main()
│	/go/src/playground/backend/cmd/server/server.go:203 +0x33

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[vchunikhin]

PROPERTY_PATH was added for every docker file to avoid problems when we will use properties.yaml for runners (JAVA, PYTHON, SCIO, GO)

[vchunikhin]

R: @pabloem

[github-actions]

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control

[pabloem]

lgtm thanks!