feat(collapse): custom display styles

[brunocroh]

Added feature of issue #2473

• read and followed the CONTRIBUTING.md guide.
• built and tested the changes
• added/updated API documentation.
• added/updated demos.

[codecov]

Codecov Report

Merging #2893 into development will increase coverage by 0.01%.
The diff coverage is 100%.

@@              Coverage Diff               @@
##           development   #2893      +/-   ##
==============================================
+ Coverage        70.69%   70.7%   +0.01%     
==============================================
  Files              137     137              
  Lines             4159    4161       +2     
  Branches           735     735              
==============================================
+ Hits              2940    2942       +2     
  Misses             914     914              
  Partials           305     305

Impacted Files	Coverage Δ
src/collapse/collapse.directive.ts	90.24% <100%> (+0.5%)	⬆️

---

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 479b046...436530d. Read the comment docs.

[valorkin]

@brunocroh hey, thanks for PR, we are cutting of v2 of ngx-bs, and dropping ng v2 support
so we will add customizable Animation support