chore: docs in the monorepo

[ludamad]

Description

Resolves #1085. Documentation should be owned more by engineers, right now
it's hard to iterate the examples easily. As well we want to avoid code-rot
by automatically updating examples.

History has been rewritten to maintain valid issue and PR links.

Redoing #1120

EDIT FOR POSTERITY: Process was similar to the below (although this exact script was for barretenberg):

set -xue
# Clone both repositories
git clone https://github.com/AztecProtocol/barretenberg.git
git clone https://github.com/AztecProtocol/aztec-packages.git

# Enter barretenberg repository and filter it
cd barretenberg
git filter-repo --to-subdirectory-filter barretenberg
git filter-repo --message-callback """
  import re

  def replace_hash_with_url(text):
       url_format = 'https://github.com/AztecProtocol/barretenberg/issues/{}'
       # the regular expression pattern r'#(\d+)' matches a '#' followed by one or more digits (\d+)
       return re.sub(r'#(\d+)', lambda match: url_format.format(match.group(1)), text)
  message = message.decode('utf-8') # Decode from bytes to string
  message = message.replace('(#', '(https://github.com/AztecProtocol/barretenberg/pull/')
  message = message.replace('Merge pull request #', 'Merge pull request https://github.com/AztecProtocol/barretenberg/pull/')
  return replace_hash_with_url(message).encode('utf-8') # Encode back into bytes
"""

# Enter aztec-packages repository
cd ../aztec-packages

# Create a new branch for the combined history
git checkout -b combined_history

# Add barretenberg as a remote and fetch it
git remote add barretenberg ../barretenberg
git fetch barretenberg

# Merge the histories, preserving the directory structure
git merge --no-commit --allow-unrelated-histories barretenberg/master

# Commit the changes
git commit -m "chore: barretenberg in the monorepo" -m "See #1126 for motivation."

Checklist:

• I have reviewed my diff in github, line by line.
• Every change is related to the PR description.
• I have linked this pull request to the issue(s) that it resolves.
• There are no unexpected formatting changes, superfluous debug logs, or commented-out code.
• The branch has been merged or rebased against the head of its merge target.
• I'm happy for the PR to be merged at the reviewer's next convenience.