Client-Spec: Umbrella issue for all TODOs

[tracymiranda]

Description

This issue is the umbrella issue that lists all the pending todos for when the spec was migrated from google docs to markdown (in same order as they appear in the doc) and anything captured in the PR review #9

• Client-Spec: 2.1.3. Certificate Issuance TODO #10
• Client-Spec: TODO review policy taxonomy #11
• Review 3.1 Signing Choices repetitiveness with earlier sections (link)
• Emphasize recommended default link
• 4.1 Inputs: consider strengthening language substantially (link)
• 4.2 do we need to include the note to implementers?
• Client-Spec: 4.2.1 Timestamping Service - update section to clarify abort behavior on parsing fails. #18
• 4.3 Resolve comment
• 4.3 Consider adding something on if no time is available (link)
• 4.3 Consider mentioning verifying other OID claims for CI/CD platforms (link)
• 4.3 Update section to mandate verifying inclusion proofs (link)
• Client-Spec: Add in link to relevant docs on revocation and expiration #8
• Client spec: post-issuance leaf check clarifications #14
• Client-spec: Review signer terminology #17