Create categories page

[simonychuang]

Adds first iteration of page in core to manage content categories. Allows basic CRUD operation with only the name field for now. Similar to Assets page categories management. UI will be improved in the next cycle, right now it's a very barebones implementation just to get the functionality in.

/nocl

How Has This Been Tested?

Tested manually on local env

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[ryan-carroll-graylog]

Basic functionality looks solid! I know there was talk about having the basic ability to add an entity id/type to a group, i.e. 2 more fields that take a type string/id combo and add to add to a group. But I don't think it's super important at this stage if there's other cycle work.

Just left one other comment about possibly tweaking the menu item name.

[ryan-carroll-graylog]

Seems to fit the pattern of the other items here to just have Entity Groups, with Manage being implied?

Suggested change

	{ path: Routes.SYSTEM.ENTITYGROUPS.OVERVIEW, description: 'Manage Entity Groups' },
	{ path: Routes.SYSTEM.ENTITYGROUPS.OVERVIEW, description: 'Entity Groups' },

[simonychuang]

@ryan-carroll-graylog Yup, that thought definitely crossed my mind but without any mockups at the moment and with the plan to continue working on this next cycle I decided to leave out the fields to add entities to a group for now.

[ryan-carroll-graylog]

Ah ok definitely makes sense to me to wait for mockups. The API is pretty simple for anyone wanting to use this as is anyway.