Add a specific deployment tier field to each host

[P-T-I]

During LS deployment this year we've worked with tier levels as tags; however it would be nice to have a dedicated field in the customization specs for the deployment tier rather then using a tag.

• The field should be able to be auto-generated (just like the tags).
• The field should only have CRUD capabilities for specific users / roles.
• The deployment tier should have a dedicated API endpoint; preferably in the following example format:

{'Tier0A': ['r-isp1'],
 'Tier0B': ['r-isp2'],
 'Tier1A': ['HOST_A', 'HOST_AA', 'HOST_AAA'],
 'Tier2A': ['HOST_B', 'HOST_BB', 'HOST_BBB'],
 'Tier3A': ['HOST_C',
            'HOST_CC',
            'HOST_CCC||5'],
}

• 'HOST_CCC||5' is the syntax for 5 sequences of 'HOST_CCC'

• Should be visible in the GUI inventory overview (just as the tags)
• Should be limited to a single entry (no multiple tier levels allowed)

[P-T-I]

@mromulus how are you? All good? Are you planning on incorporating #485, #486 and #487 before the execution of this years' LS?