sagemathgh-37977: Add a method to enumerate cographs

    
As suggested in sagemath#37964, this PR add a method to enumerate cographs of
order `n`. We add a new file that could collect all methods related to
cographs (enumeration, random generator, identification, etc.).

The original implementation is due to Marianna Spyrakou
(https://github.com/MariannaSpyrakou/Cograph_generator).


### 📝 Checklist

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- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [x] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

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URL: sagemath#37977
Reported by: David Coudert
Reviewer(s): David Coudert, Travis Scrimshaw

src/doc/en/reference/graphs/index.rst

@@ -78,6 +78,7 @@ Libraries of algorithms
    sage/graphs/centrality
    sage/graphs/asteroidal_triples
    sage/graphs/independent_sets
+   sage/graphs/cographs
    sage/graphs/comparability
    sage/graphs/line_graph
    sage/graphs/spanning_tree

src/doc/en/reference/references/index.rst

@@ -3638,6 +3638,11 @@ REFERENCES:
 .. [Jon2005] \V. Jones, The Jones Polynomial, 2005.
              https://math.berkeley.edu/~vfr/jones.pdf
 
+.. [JPD2018] Átila A. Jones, Fábio Protti and Renata R. Del-Vecchio:
+             *Cograph generation with linear delay*.
+             Theoretical Computer Science, 713:1-10, 2018.
+             :doi:`10.1016/j.tcs.2017.12.037`
+
 .. [JRJ94] Jourdan, Guy-Vincent; Rampon, Jean-Xavier; Jard, Claude
            (1994), "Computing on-line the lattice of maximal antichains
            of posets", Order 11 (3) p. 197-210, :doi:`10.1007/BF02115811`