Remove antiquated msmtp and ntfy images (borgmatic-collective#240)

* Remove antiquated msmtp and ntfy images

Signed-off-by: Chirag Aggarwal <[email protected]>

* Updated IMAGE_ARCHITECTURE.md

Signed-off-by: Chirag Aggarwal <[email protected]>

* Added news regarding discontinuation of flavors

Signed-off-by: Chirag Aggarwal <[email protected]>

* Allow running as binary without cron

Signed-off-by: Chirag Aggarwal <[email protected]>

* Allow container to stop gracefully

Signed-off-by: Chirag Aggarwal <[email protected]>

* Current README progress

Signed-off-by: Chirag Aggarwal <[email protected]>

* minor fixes

Signed-off-by: Chirag Aggarwal <[email protected]>

* CRON ENV VAR | RUN_ON_STARTUP | README progress

Signed-off-by: Chirag Aggarwal <[email protected]>

* formatting

Signed-off-by: Chirag Aggarwal <[email protected]>

* Update README.md

* Remove link flag

Signed-off-by: Chirag Aggarwal <[email protected]>

* Update .gitignore

Based on borgmatic-collective#240 (comment)

* Update README.md

* Crontab.txt related edits

* Update README.md

* Update requirements.txt

* Remove antiquated msmtp and ntfy images

Signed-off-by: Chirag Aggarwal <[email protected]>

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Signed-off-by: Chirag Aggarwal <[email protected]>
Co-authored-by: Grant Bevis <[email protected]>