Add trigger `onstartup`

[Dirreke]

Add trigger onstartup, ref: log4j

[estk]

@bconn98 can you please review, this seem like a great feature to add , also @Dirreke I think you'll need to rebase to get that check to pass

[bconn98]

@estk Yup will do, I was waiting on the checks. Hadn't looked close enough to realize it was just the 1.67 issue

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 63.56%. Comparing base (8ab1b34) to head (bfe961e).

Files	Patch %	Lines
.../rolling_file/policy/compound/trigger/onstartup.rs	81.81%	2 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #343 +/- ## ========================================== + Coverage 63.39% 63.56% +0.17% ========================================== Files 24 25 +1 Lines 1557 1570 +13 ========================================== + Hits 987 998 +11 - Misses 570 572 +2 ```

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[Dirreke]

It can also close #250 .

[estk]

@Dirreke thanks for your continued work hard work on this. One last comment, but looking excellent otherwise!

[Dirreke]

Thanks. I don't have envs at the moment. I think I will do it after 02/16.

[Dirreke]

Bump MSRV to 1.70 for toml

[estk]

Only concern I have here is bumping MSRV, the goal is to support at least a year old compiler. Any way we can avoid that?

[bconn98]

Toml started bumping like crazy. I locked it in my branches at the current, but we can lock it at the previous and maintain 1.69.

[Dirreke]

I will rebase it after #354

[bconn98]

Feel free to rebase now @Dirreke