Specify labels via a command-line option (rather than hardcoding)

[joshuacwnewton]

Currently, we hardcode the "PR category" labels for projects in the source code for changelog:

changelog/changelog/changelog.py

Lines 303 to 321 in cfd5baa

	# provides customization to changelog for some repos
	options = {
	'default': {
	'labels': [None],
	'generator': default_changelog_generator,
	},
	'spinalcordtoolbox': {
	'labels': ['feature', 'documentation-internal', 'CI', 'bug', 'installation', 'documentation', 'enhancement', 'refactoring', 'git/github'],
	'generator': sct_changelog_generator,
	},
	'ivadomed': {
	'labels': ['bug', 'dependencies', 'documentation', 'enhancement'],
	'generator': default_changelog_generator,
	},
	'axondeepseg': {
	'labels': ['bug', 'enhancement', 'feature', 'documentation', 'installation', 'testing'],
	'generator': default_changelog_generator,
	}
	}

Doing it this way forces each project to open up a PR if they want to modify how their changelog is generated. (e.g. #28).

Instead, perhaps we could have the usage look like this:

changelog --repo-url ivadomed/ivadomed --labels feature bug installation documentation enhancement [...]

That way, changelog stays project-agnostic, and each project doesn't have to open a PR every time they make a change to their label scheme. 😅