instruments/trace_cmd: Add tracing mode support to TraceCmdInstrument()

Implement tracing mode support (mainly for write-to-disk mode) in
TraceCmdInstrument, enabling efficient collection of large trace
datasets without encountering memory limitations.

This feature is particularly useful for scenarios requiring extensive
trace data.

Additional changes:
- Replace hardcoded strings with corresponding string literals for
  improved maintainability.

Signed-off-by: Metin Kaya <metin.kaya@arm.com>

doc/source/user_information/user_guide.rst

@@ -400,6 +400,7 @@ below:
                 no_install: false
                 report: true
                 report_on_target: false
+                mode: write-to-memory
             csv:
                 extra_columns: null
                 use_all_classifiers: false

doc/source/user_information/user_reference/agenda.rst

@@ -45,6 +45,7 @@ An example agenda can be seen here:
             no_install: false
             report: true
             report_on_target: false
+            mode: write-to-disk
         csv:                    # Provide config for the csv augmentation
             use_all_classifiers: true