[cmake] Disable mon plugin and rec addon sdks by default unless building apps

[DownerCase]

Description

Disables building the monitor plugin and rec addon unless BUILD_APPS is on.

These options are not part of eCAL core and aren't needed in a minimal configuration.

An option is made for the rec_addon but not the monitor plugin because the monitor app requires it. I presume it is unlikely one would want to use a local build to make a plugin but not build the gui app itself.

Related issues

closes #380

Cherry-pick to

[KerstinKeller]

Both options do make a lot of sense.
This might allow to remove the paths in pyproj.toml also:

ecal/pyproject.toml

Lines 47 to 48 in 6c9a238

	"/app/rec/rec_addon_core/", # TODO: Remove this directory
	"/app/rec/rec_addon_dummy/", # TODO: Remove this directory

[DownerCase]

This might allow to remove the paths in pyproj.toml also:

ecal/pyproject.toml

Lines 47 to 48 in 6c9a238

	"/app/rec/rec_addon_core/", # TODO: Remove this directory
	"/app/rec/rec_addon_dummy/", # TODO: Remove this directory

Absolutely! Will check if the app/apps folder can be sorted too.

[KerstinKeller]

We had previously used the app names in eCAL core, and thus always needed that folder. This dependency is no longer there, so it's fine to have that only when we have BUILD_APPS activated.