ENH: Add --force option to script tools/update_schema

[slangeveld]

Resolving #740

Adds a new argument --force to the tools/update_schema script that is used to update fmu_meta.json schema.

This has been added to have a way to force an overwrite of the current json schema, if the current json schema has been malformed for some reason, e.g. because of a merge conflict.

Changes :

1. --force has been added as a new valid argument to the script
2. When running the script with the --force argument, the script will skip checking/validating the current schema and overwrite with the new one.
3. In case of a json parsing error of the current json schema, the script will exit and inform the user about the possibility of running the script with the --force argument.

Local testing
The changes has been testes locally by:

1. Editing the current schema fmu_meta.json to be an unvalid json, followed by running the script to see that the json parse error was outputted to the user, in addition to the suggestion of running the script with the --force argument.
2. Running the script with the new argument --force to see if the schema was overridden.

[mferrera]

Nice 👍 I think the we should give a fail exit status when json parsing is fails but otherwise good to go

[mferrera]

Suggested change

	sys.exit()
	sys.exit(1)

I think it'd be good to indicate an error status with the exit code

[slangeveld]

Good point. Will add that