Split ctfd_challenge in two separate resources

[pandatix]

After #133, this PR would introduce breaking changes.
The reflection behind it comes from #131.

Inside this PR I drop ctfd_challenge in favor of 2 new resources:

• ctfd_challenge_standard
• ctfd_challenge_dynamic

Additionally to the features discussed in the issue (TL;DR better documentation, maintainability, and autocompletion), the internals changed toward a better fit of the CTFd API, and ease development of other providers for plugins.
For instance, when conceiving the Terraform provider for the ctfd-chall-manager plugin we would be able to reuse the ChallengeStandardResourceModel structure and ChallengeStandardResourceAttributes variable, in the way I implemented the ctfd_challenge_dynamic.

Reusing the ID for other resources (e.g. ctfd_file, ctfd_flag) is still possible.

Poke @Nishacid. I know you used it for GreHack24, your feedback on such an evolution would be welcome 😄

[coveralls]

Pull Request Test Coverage Report for Build 12297700719

Details

• 338 of 503 (67.2%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-2.7%) to 67.428%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
provider/challenge_common.go	9	15	60.0%
provider/challenge_standard_data_source.go	5	13	38.46%
provider/challenge_dynamic_data_source.go	83	121	68.6%
provider/challenge_dynamic_resource.go	207	320	64.69%

Totals
Change from base Build 12144207231:	-2.7%
Covered Lines:	1594
Relevant Lines:	2364

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💛 - Coveralls

[NicoFgrx]

LGTM