Add UpdateCommand

[Giuspepe]

Fixes #96

Scope of this PR

• pubspec.yaml template now contains a field sidekick: cli_version: <version> which contains the sidekick version the CLI was generated with
• Checks whether an update is available whenever a command is executed
• Add UpdateCommand which calls the latest available version of update_sidekick_cli.dart
• update_sidekick_cli currently updates the following:
  • shell scripts in tool (download_dart.sh, install.sh, run.sh, sidekick_config.sh)
  • entrypoint executable
  • sidekick_core dependency to latest available version
  • sidekick->cli_version in pubspec.yaml to latest available sidekick version

Necessary work in following PRs

Update sidekick_core in sidekick and pass new sidekick version parameter to SidekickTemplateProperties

When generating a new sidekick CLI package, we have to save the version of sidekick which generated the CLI in the generated CLI's <generated-cli>/pubspec.yaml. However, we can't read the global sidekick's version because its executable is compiled and thus does not have access to its own <global-sidekick>/pubspec.yaml because it isn't bundled with the compiled executable.
Instead we could use an automatically generated source file which contains the version information
See e.g. https://stackoverflow.com/a/69048343/9905602 or how mason_cli implements this in a version.dart file: https://github.com/felangel/mason/pull/538/files

We should save the version of sidekick_core from sidekick's pubspec.lock in a Dart file

Add migration functions

Whenever additional steps (besides regenerating shell scripts) are needed to migrate from an old to the latest version, add them to update_sidekick_cli.dart. This script receives the current and the latest version. This information can be used to call migration functions to do additional update steps (e.g. modifying certain lines in dart files).

How to test this PR

There is a update_command_test.dart which already tests this command.
If you want to test this manually, do the following:

1. Edit the pubspec.yaml of an old sidekick CLI

dependencies:
  sidekick_core: '>=0.11.0 <1.0.0'

dependency_overrides:
  sidekick_core:
    path: /Users/pepe/repos/sidekick/sidekick_core

2. Add SidekickCommand to the cli
3. Run <cli> sidekick update
4. Verify the following:
   1. the 4 shell scripts in tool have been updated
   2. cli_version has been updated to the latest version of sidekick (0.7.1)
   3. the sidekick_core dependency has been updated to sidekick_core: '>=0.11.1 <1.0.0'
   4. A success message has been printed (Successfully updated sidekick CLI <cli> from version 0.0.0 to 0.7.1!)

[Giuspepe]

Maybe we should also uses this command to update the bundled dart runtime (sidekickDartRuntime). See #57

[Giuspepe]

When running <cli> sidekick update as described above in an outdated sidekick CLI almost everything works. This is the output:

Updating sidekick CLI iv from version 0.0.0 to 0.7.1 ...
Successfully updated sidekick CLI iv from version 0.0.0 to 0.7.1!
/Users/pepe/repos/invo-frontend/packages/iv_sidekick/tool/run.sh: line 70: unexpected EOF while looking for matching `"'

Everything is correctly updated and executed from the dart side, but an error (exit code 2) is thrown from the run.sh script:

/Users/pepe/repos/invo-frontend/packages/iv_sidekick/tool/run.sh: line 70: unexpected EOF while looking for matching `"'

I guess because we're modifying the file which is currently being executed? 🤔