feat: more options for UI middleware

[fredbi]

• refactored UI middleware

  • factorized UI middleware to remove duplicated code
  • factorized UI middleware options: to avoid breaking changes in the options types, there is a decode/encode to a common structure
  • added more options:
  • allows to fully customize the UI template
  • added more unit tests

• Spec middleware: added support for optional SpecOption argument

  • allows to serve the spec from a custom path / document name

• serving with or without trailing "/" (cf. issue #238)

  • replaced path.Join() by path.Clean(), which is the intended behavior (i.e. serve the path, irrespective of the presence of a trailing slash)
  • generalized this behavior to all UI and Spec middleware, not just swaggerUI

• API Context:

  • exposed middleware to serve RapiDoc UI
  • allowed new UIOption (...UIOption) to the APIHandler, etc middleware
  • coordinated UI / Spec middleware to be consistent when non-default path/document URL is served

• fixes #192

• fixes #226

[codecov[bot]]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (248b38c) 80.83% compared to head (f3145ae) 82.04%.

Files	Patch %	Lines
middleware/ui_options.go	85.00%	8 Missing and 4 partials :warning:
middleware/context.go	95.00%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #278 +/- ## ========================================== + Coverage 80.83% 82.04% +1.20% ========================================== Files 44 45 +1 Lines 3366 3420 +54 ========================================== + Hits 2721 2806 +85 + Misses 535 501 -34 - Partials 110 113 +3 ``` | [Flag](https://app.codecov.io/gh/go-openapi/runtime/pull/278/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=go-openapi) | Coverage Δ | | |---|---|---| | [oldstable](https://app.codecov.io/gh/go-openapi/runtime/pull/278/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=go-openapi) | `82.04% <92.89%> (+1.20%)` | :arrow_up: | | [stable](https://app.codecov.io/gh/go-openapi/runtime/pull/278/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=go-openapi) | `82.04% <92.89%> (+1.20%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=go-openapi#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.