Improve `cbuild` help text

[ReinhardKeil]

The Problem To Be Solved

• For cbuild2cmake: remove "(default true)"
• For jobs: add "(default 8)" as this seems to be the default value
• For load: add "(default required)" as I believe this is the default
• Remove when possible buildcprj from help text, as we are going to deprecate this feature (I know that Go has perhaps restrictions here).

Usage:
  cbuild [command] <name>.csolution.yml [options]

Commands:
  help        Help about any command
  list        List information about environment, toolchains, and contexts
  setup       Generate project data for IDE environment

Options:
      --cbuild2cmake       Use build information files with cbuild2cmake backend (default)
      --cbuildgen          Use build information files with cbuildgen backend
  -C, --clean              Remove intermediate and output directories
  -c, --context arg [...]  Input context names [<project-name>][.<build-type>][+<target-type>]
  -S, --context-set        Select the context names from cbuild-set.yml for generating the target application
  -d, --debug              Enable debug messages
      --frozen-packs       Pack list and versions from cbuild-pack.yml are fixed and raises errors if it changes
  -g, --generator arg      Select build system generator (default "Ninja")
  -h, --help               Print usage
  -j, --jobs int           Number of job slots for parallel execution (default 8)
  -l, --load arg           Set policy for packs loading [latest | all | required] (default required)

[soumeh01]

The changes are made and the usage looks like

Usage:
  cbuild [command] <name>.csolution.yml [options]

Commands:
  help        Help about any command
  list        List information about environment, toolchains, and contexts
  setup       Generate project data for IDE environment

Options:
      --cbuild2cmake       Use build information files with cbuild2cmake backend (default)
      --cbuildgen          Use build information files with cbuildgen backend
  -C, --clean              Remove intermediate and output directories
  -c, --context arg [...]  Input context names [<project-name>][.<build-type>][+<target-type>]
  -S, --context-set        Select the context names from cbuild-set.yml for generating the target application   
  -d, --debug              Enable debug messages
      --frozen-packs       Pack list and versions from cbuild-pack.yml are fixed and raises errors if it changes
  -g, --generator arg      Select build system generator (default "Ninja")
  -h, --help               Print usage
  -j, --jobs int           Number of job slots for parallel execution (default 8)
  -l, --load arg           Set policy for packs loading [latest | all | required] (default "required")
      --log arg            Save output messages in a log file
  -O, --output arg         Set directory for all output files
  -p, --packs              Download missing software packs with cpackget
  -q, --quiet              Suppress output messages except build invocations
  -r, --rebuild            Remove intermediate and output directories and rebuild
  -s, --schema             Validate project input file(s) against schema
  -t, --target arg         Optional CMake target name
      --toolchain arg      Input toolchain to be used
      --update-rte         Update the RTE directory and files
  -v, --verbose            Enable verbose messages from toolchain builds
  -V, --version            Print version

Use "cbuild [command] --help" for more information about a command.