Document Noir smart contract syntaxes

[Savio-Sou]

As the v0.9.0 release deprecates the --experimental-ssa flag (i.e. all Noir smart contract syntaxes would be supported out of the box), it'd be best to document the syntaxes alongside the release.

Relevant PRs:

• contract
  Retroactive: Noir contract scope noir#1135
  feat: Implement basic contracts noir#944
  fix: Prevent calling contract functions from outside the contract noir#980
• function visibilities
  Retroactive: Add Noir contract function types noir#1168
  • open functions
    feat: Implement 'open' and 'unconstrained' keywords noir#1037
  • internal functions
    feat: Adding internal keyword noir#1873
• secret functions can have pub values
  feat: Allow secret functions to use public parameters noir#1051

P.S. The Aztec libraries for smart contract utilities, albeit written in Noir, are probably more suiting to be documented in Aztec's docs.

[critesjosh]

I will connect with Mike on starting this section, as it is planning to be added to the Aztec docs as well.

[Savio-Sou]

Closing as it'll be documented in the Aztec Docs instead.