Week -1: follow-up emails

[celiala]

This PR adds follow-up emails for:

• the day before PrepDate (to be sent if only there are still blockers)
• the day of PrepDate (to be sent if only there are still blockers)
• the day after PrepDate (to be sent if only there are still blockers)

The post-blockers command should be used for all emails before and up to PrepDate:

# where `DAYS_BEFORE_PREP` is one of: many-days | day-before | day-of

SMTP_PASSWORD=$MY_SMTP_PWD SMTP_USER=$MY_SMTP_USER GITHUB_TOKEN=$MY_GITHUB_TOKEN \
$(bazel info bazel-bin)/pkg/cmd/release/release_/release post-blockers \
  --release-series 21.1 \
  --smtp-user $MY_SMTP_USER --smtp-host smtp.gmail.com --smtp-port 587 \
  --to $MY_TO_EMAIL \
  --template-dir ./pkg/cmd/release/templates \
  --prep-date "Apr 1, 2022" --publish-date "May 1, 2022" \
  --days-before-prep-date $DAYS_BEFORE_PREP

The cancel-release-date should be used for the day after PrepDate email:

SMTP_PASSWORD=$MY_SMTP_PWD SMTP_USER=$MY_SMTP_USER GITHUB_TOKEN=$MY_GITHUB_TOKEN \
$(bazel info bazel-bin)/pkg/cmd/release/release_/release cancel-release-date \
  --release-series 21.1 \
  --smtp-user $MY_SMTP_USER --smtp-host smtp.gmail.com --smtp-port 587 \
  --to $MY_TO_EMAIL \
  --template-dir ./pkg/cmd/release/templates \
  --publish-date "May 1, 2022" --next-publish-date "Jun 1, 2022"

TeamCity changes

This will be paired with the following TeamCity jobs:

• Send release blockers - 78595
• Cancel release date - 78595

Manual tests

Test 1: post-blockers --days-before-prep-date many-days

Test 2: post-blockers --days-before-prep-date day-before

Test 3: post-blockers --days-before-prep-date day-of

Test 4: cancel-release-date

[cockroach-teamcity]

This change is 

[celiala]

Hi @rail - I thought I could get these emails up in time for us to run today's "Monday emails" step, but the new parameters don't seem to be wired up correctly 🤔 . See failed attempts:

https://teamcity.cockroachdb.com/buildConfiguration/Internal_Cockroach_Release_Process_SendReleaseBlockers_78595?branch=78595&mode=builds#all-projects

Maybe we can chat about this further in today's weekly release meeting.

[celiala]

Hi @rail - I just squashed -- this is RFAL whenever you have a moment, thank you!

[rail]

Reviewed 42 of 42 files at r1, 4 of 4 files at r2, 1 of 1 files at r3, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @celiala)

[celiala]

TFTR!

bors r=rail

[craig]

Build succeeded:

• GitHub CI (Cockroach)