acme: add context cancellation

[codecov-commenter]

Codecov Report

Patch coverage: 90.47% and project coverage change: +0.04 :tada:

Comparison is base (9ddad35) 74.11% compared to head (26f51c6) 74.16%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #314 +/- ## ========================================== + Coverage 74.11% 74.16% +0.04% ========================================== Files 43 43 Lines 4849 4858 +9 ========================================== + Hits 3594 3603 +9 Misses 1008 1008 Partials 247 247 ``` | [Impacted Files](https://app.codecov.io/gh/komuw/ong/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Komu+Wairagu) | Coverage Δ | | |---|---|---| | [internal/acme/acme.go](https://app.codecov.io/gh/komuw/ong/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Komu+Wairagu#diff-aW50ZXJuYWwvYWNtZS9hY21lLmdv) | `66.77% <82.75%> (+1.97%)` | :arrow_up: | | [internal/acme/client.go](https://app.codecov.io/gh/komuw/ong/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Komu+Wairagu#diff-aW50ZXJuYWwvYWNtZS9jbGllbnQuZ28=) | `59.75% <96.55%> (ø)` | | | [internal/acme/helpers.go](https://app.codecov.io/gh/komuw/ong/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Komu+Wairagu#diff-aW50ZXJuYWwvYWNtZS9oZWxwZXJzLmdv) | `65.29% <100.00%> (-1.12%)` | :arrow_down: | | [internal/acme/http\_client.go](https://app.codecov.io/gh/komuw/ong/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Komu+Wairagu#diff-aW50ZXJuYWwvYWNtZS9odHRwX2NsaWVudC5nbw==) | `69.18% <100.00%> (ø)` | |

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