Gabe extra provision attributes

[byxorna]

This PR adds support for collins to add/remove arbitrary attributes on an asset at provision time, on a per-nodeclass basis. I.e. lets say you want to tag all nodes that are development hosts with DEVELOPMENT_MODE=true, you could put this in profiles.yaml to have that attribute automatically set at provision time.

---
profiles:
    devdbnode:
        label: "Dev DB Node"
        prefix: "devdb"
        attributes:
            development_mode: true
    devnode:
        label: "Dev Node"
        prefix: "dev"
        attributes:
            development_mode: true

Similarly, you can clear specific attributes on specific nodeclasses, if you want to ensure there are no undesirable effects at provision time. (i.e. DEVELOPMENT_MODE attribute creates undesirable behavior on your production DB nodes):

---
profiles:
    proddbnode:
        label: "Prod DB Node"
        prefix: "db"
        clear_attributes:
          - development_mode
          - some_attribute_that_most_nodes_want_but_not_proddbs

The was this is written such that attributes specified in clear_attributes wont clobber any more important attrs set by collins (i.e. nodeclass). The ordering of what trumps what is, in order of trumpiness:

1. attrs set explicitly by collins during provision (nodeclass, build_contact, pool, etc) from the profile
2. attributes set in the attributes map in profile
3. attributes to clear on a nodeclass from clear_attributes in profile
4. attributes collins will clear on all assets (Feature.deleteSomeMetaOnRepurpose)

Let me know what you guys think!

[byxorna]

@maddalab @dallasmarlow @Primer42

[william-richard]

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