[WIP] feat: support Views API

[suzuki-shunsuke]

issue: #182

[codecov]

Codecov Report

Merging #183 into master will decrease coverage by 0.42%.
The diff coverage is 43.06%.

@@            Coverage Diff             @@
##           master     #183      +/-   ##
==========================================
- Coverage   52.96%   52.54%   -0.43%     
==========================================
  Files         126      130       +4     
  Lines        6062     6336     +274     
==========================================
+ Hits         3211     3329     +118     
- Misses       2657     2813     +156     
  Partials      194      194              

Impacted Files	Coverage Δ
graylog/client/endpoint/view.go	0.00% <0.00%> (ø)
graylog/graylog/view.go	0.00% <0.00%> (ø)
graylog/client/view.go	16.12% <16.12%> (ø)
graylog/terraform/resource_view.go	63.42% <63.42%> (ø)
graylog/client/endpoint/endpoint.go	82.35% <100.00%> (+0.35%)	⬆️
graylog/terraform/provider.go	97.29% <100.00%> (+0.03%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a26bd26...b5da60b. Read the comment docs.

[suzuki-shunsuke]

hashicorp/terraform-plugin-sdk#62

Oh, we have to fix state.

https://pkg.go.dev/github.com/hashicorp/terraform/helper/schema?tab=doc#Schema

For a TypeMap, it must be a *Schema with a Type that is one of the primitives: TypeString, TypeBool, TypeInt, or TypeFloat