lib: os: cbprintf: Extend API to support new packaging modes

Added new flags to packaging API:
- CBPRINTF_PACKAGE_ADD_RO_STR_IDXS - when set, read-only string
  locations are appended to the package
- CBPRINTF_PACKAGE_ADD_RW_STR_IDXS - when set, read-write string
  locations are appended to the package (instead of appending actual
  strings)
- CBPRINTF_PACKAGE_FIRST_RO_STR_CNT(n) - indicate that n first strings
  are known to be read only. Ignored in runtime packaging.

Add function for copying packages with optional appending strings.

Changed CBPRINTF_MUST_RUNTIME_PACKAGE to use same flags as packaging.

Aligned logging and test to those changes.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>