Generate API docs

[penelopeysm]

Description

This PR generates API docs for Turing.jl itself. This exposes documentation for important things like samplers which are otherwise undocumented.

Many of the exported identifiers are defined in other packages (DynamicPPL, etc.) and re-exported and/or extended by Turing. Rather than inserting the actual docs (which can actually be quite difficult sometimes as it requires locating the right method), I've generally opted to put them in a table with links to the corresponding package documentation.

This PR also adds docstrings to exported identifiers where necessary, and fixes some inaccuracies in the MH() docstrings.

Closes #2344.

Preview the docs

https://turinglang.org/Turing.jl/previews/PR2347/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (40a0d84) to head (446f278).

❗ There is a different number of reports uploaded between BASE (40a0d84) and HEAD (446f278). Click for more details.

HEAD has 16 uploads less than BASE

Flag	BASE (40a0d84)	HEAD (446f278)
	56	40

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #2347       +/-   ##
==========================================
- Coverage   86.67%   0.00%   -86.68%     
==========================================
  Files          24      22        -2     
  Lines        1599    1533       -66     
==========================================
- Hits         1386       0     -1386     
- Misses        213    1533     +1320     

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[coveralls]

Pull Request Test Coverage Report for Build 11252307560

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1325 unchanged lines in 21 files lost coverage.
• Overall coverage decreased (-87.0%) to 0.0%

---

Files with Coverage Reduction	New Missed Lines	%
src/variational/VariationalInference.jl	4	0.0%
src/Turing.jl	9	0.0%
src/mcmc/gibbs_conditional.jl	12	0.0%
src/mcmc/is.jl	16	0.0%
src/stdlib/RandomMeasures.jl	22	0.0%
src/essential/container.jl	27	0.0%
ext/TuringDynamicHMCExt.jl	29	0.0%
src/mcmc/emcee.jl	47	0.0%
ext/TuringOptimExt.jl	50	0.0%
src/mcmc/ess.jl	51	0.0%

Totals
Change from base Build 11180921169:	-87.0%
Covered Lines:	0
Relevant Lines:	1533

---

💛 - Coveralls

[penelopeysm]

I think this is finally ready :) Most of the changes can be seen via the preview docs (https://turinglang.org/Turing.jl/previews/PR2347/) but also please do check over the docstrings I added.

(There are no source code changes in this PR)

[yebai]

@sunxd3 can you help review @penelopeysm's PR?

[penelopeysm]

1.11 tests failing because of compintell/Mooncake.jl#180

[sunxd3]

Great work @penelopeysm

[sunxd3]

ideally, this page is more structured. but I think we should merge this now and fix it later.