fix: handle column and derived column imports with slashes in the name

[jharley]

Some columns and derived columns have slashes in the name. Prior to this change, trying to import either with slashes in the name would result in a message like:

$ terraform import 'honeycombio_column.test' 'test/my/column/name'
honeycombio_column.test: Importing from ID "test/my/column/name"...
honeycombio_column.test: Import prepared!
  Prepared honeycombio_column for import
honeycombio_column.test: Refreshing state... [id=test/my/column/name]
╷
│ Error: Cannot import non-existent remote object
│
│ While attempting to import an existing object to "honeycombio_column.test", the provider detected that no object exists with the given id. Only pre-existing objects can be imported; check that the id is correct
│ and that it is associated with the provider's configured region or endpoint, or use "terraform apply" to create a new remote object for this resource.
╵

Most (all?) other resources are imported by ID, but this subtle change in splitting does the trick here.

[jharley]

unrelated, but snuck this in as the test was broken locally

[codecov-commenter]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (d92499c) 83.19% compared to head (1365236) 83.20%.

Files	Patch %	Lines
honeycombio/resource_slo.go	0.00%	3 Missing ⚠️
honeycombio/resource_column.go	33.33%	1 Missing and 1 partial ⚠️
honeycombio/resource_derived_column.go	33.33%	1 Missing and 1 partial ⚠️
internal/provider/trigger_resource.go	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #437   +/-   ##
=======================================
  Coverage   83.19%   83.20%           
=======================================
  Files          62       62           
  Lines        4178     4168   -10     
=======================================
- Hits         3476     3468    -8     
+ Misses        549      547    -2     
  Partials      153      153           

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