Fix handling of script arguments in tracer

[lantiga]

What does this PR do?

TracerPythonScript assumes that additional params start with --

For instance, passing params={"a": 1} is turned into script_args == "--a=1". This breaks when this assumption is not true, for instance when parsing arguments using hydra.cc

This PR removes this assumption. The (unavoidable) downside is a params argument needs to be provided as {"--a": 1} if it is meant to be turned into --a=1, otherwise it is converted to a=1.

Note that this is needed for Lightning-Universe/Training-Studio_app#216 to work

Fixes #<issue_number>

Does your PR introduce any breaking changes? If yes, please list them.

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[tchaton]

LGTM !

[awaelchli]

It is probably best if we make self.script_args and params both lists in the future. It seems unintuitive to be passing two different data types. The user would do the conversion outside in reverse to what we do internally.

[awaelchli]

This looks like undocumented behavior and we can probably change it, but it may break some apps.