Add certificate message and adapter

[jpraynaud]

Content

This PR adds a CertificateMessage message and adapter types.

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • No clippy warnings in the CI
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested

Issue(s)

Closes #697

[github-actions]

Test Results

    3 files  ±0    28 suites  ±0   5m 24s ⏱️ -29s
401 tests +3  401 ✔️ +3  0 💤 ±0  0 ❌ ±0 
466 runs  +5  466 ✔️ +5  0 💤 ±0  0 ❌ ±0 

Results for commit f8e7f44. ± Comparison against base commit 5679425.

This pull request removes 2 and adds 5 tests. Note that renamed tests count towards both.

message_adapters::to_register_signature_message_adapter::tests ‑ adapt_ok
message_adapters::to_register_signer_message_adapter::tests ‑ adapt_ok

message_adapters::from_certificate_message_adapter::tests ‑ adapt_ok
message_adapters::to_certificate_message::tests ‑ adapt_ok
message_adapters::to_register_signature_message::tests ‑ adapt_ok
message_adapters::to_register_signer_message::tests ‑ adapt_ok
messages::certificate::tests ‑ test_v1

♻️ This comment has been updated with latest results.