feat: Add ability to delay startup

[PurseChicken]

Describe the feature request

I would like for there to be the ability to add a delay to the image starting up before executing /gatus.

I imagine this can be done internally based on an environment variable (e.g. GATUS_SLEEP). What might be easier is to modify the dockerfile to build from golang:alpine vs scratch. This will allow the use of sh or /bin/ash so that in Kubernetes, for example, we can overwrite the entrypoint be be something like /bin/ash -c sleep 5 /gatus.

Why do you personally want this feature to be implemented?

The reason why I am looking into this is because when using a sidecar in Kubernetes (for example cloud-sql-proxy), the gatus image comes up before the sidecar does and that causes an error since the database is not available yet. A simple way to solve this is to add a configurable delay to the gatus image to give the sidecar enough time to be ready for connections.

[TwiN]

We could just add a sleep function with a configurable duration (e.g. GATUS_DELAY_START_SECONDS) at the top of the main function.

[PurseChicken]

We could just add a sleep function with a configurable duration (e.g. GATUS_DELAY_START_SECONDS) at the top of the main function.

Sounds amazing!

[vax-r]

@TwiN @PurseChicken
Hello, if this issue isn't taken yet, I would like to try to solve it

[TwiN]

@vax-r Feel free to give it a shot!
I'll assign the issue to you for now - feel free to let me know if you change your mind!

[vax-r]

Hello @TwiN , @PurseChicken
I've made some small adjustment to the code to enable this function
Please take a look if you have time, Thank you!