docs: Updates release scripts and docs

[michael-s-molina]

SUMMARY

Removes the logic to automatically send release-related emails. Now, the scripts will only generate the email content and the release manager have to manually send the emails. The objective is to avoid delivering incorrect emails to the dev list which has a big audience. The documentation was also updated with new steps related to the release.

TESTING INSTRUCTIONS

• Set the environment variables using the set_release_env.sh script
• Execute the generate_email.py script for each command (vote_pmc, result_pmc, announce)
• The script should correctly generate the email text for each command

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[villebro]

LGTM with one minor (non-blocking) suggestion. Also, I think we could change the prefix in the title to docs, as it's an improvement (not a pure chore).