Release notes 0.27.0 (#3283)

* Restructure

* fixed formating for link in GellMann observable

* another pass

* another pass

* minor

* minor

* added missing entries

* Removed extraneous missing entries, pass through pauli module entry

* return types item: add section and move it down to bottommost item; whitespace linting; qchem typo fix

* Shortened new return type entry

* minor

* added missing entries

* replace 'our demo' with another name to bypass duplicacy issue with Sphinx

* update changelog with correct vals and new repr

* minor

* Apply suggestions from code review

Co-authored-by: Diego <[email protected]>

* removed duplicate PR entries

* removed duplicate PR entries

* Apply suggestions from Tom's code review

Co-authored-by: Tom Bromley <[email protected]>

* Return types entry refactor, general restructure

* Tom

* JVP changelog

* minor

* Apply suggestions from Josh's code review

Co-authored-by: Josh Izaac <[email protected]>

* Apply suggestions from code review

Co-authored-by: Tom Bromley <[email protected]>

* minor

Co-authored-by: Jay Soni <[email protected]>
Co-authored-by: Antal Szava <[email protected]>
Co-authored-by: Matthew Silverman <[email protected]>
Co-authored-by: Diego <[email protected]>
Co-authored-by: Tom Bromley <[email protected]>
Co-authored-by: Romain Moyard <[email protected]>
Co-authored-by: Josh Izaac <[email protected]>