Increase unseal retry limit

[alemorcuq]

Description of the change
Increase the number of maximum unseal retries to 15.

The original first 5 retries happen in just 200ms, which is not enough time for some scenarios, such as the one described in #1599.
Increasing this number will ensure the exponential backoff takes off.

Here's an excerpt from the logs that shows the time at which each retry happens (starting at 1, since 0 shows the first attempt which is not a retry):

$ kubectl logs -n kube-system deploy/sealed-secrets-controller | grep Updating | nl -v 0
     0	time=2024-09-29T11:49:35.764Z level=INFO msg=Updating key=default/my-secret
     1	time=2024-09-29T11:49:35.777Z level=INFO msg=Updating key=default/my-secret
     2	time=2024-09-29T11:49:35.794Z level=INFO msg=Updating key=default/my-secret
     3	time=2024-09-29T11:49:35.822Z level=INFO msg=Updating key=default/my-secret
     4	time=2024-09-29T11:49:35.867Z level=INFO msg=Updating key=default/my-secret
     5	time=2024-09-29T11:49:35.955Z level=INFO msg=Updating key=default/my-secret
     6	time=2024-09-29T11:49:36.123Z level=INFO msg=Updating key=default/my-secret
     7	time=2024-09-29T11:49:36.451Z level=INFO msg=Updating key=default/my-secret
     8	time=2024-09-29T11:49:37.098Z level=INFO msg=Updating key=default/my-secret
     9	time=2024-09-29T11:49:38.389Z level=INFO msg=Updating key=default/my-secret
    10	time=2024-09-29T11:49:40.957Z level=INFO msg=Updating key=default/my-secret
    11	time=2024-09-29T11:49:46.088Z level=INFO msg=Updating key=default/my-secret
    12	time=2024-09-29T11:49:56.338Z level=INFO msg=Updating key=default/my-secret
    13	time=2024-09-29T11:50:16.823Z level=INFO msg=Updating key=default/my-secret
    14	time=2024-09-29T11:50:57.793Z level=INFO msg=Updating key=default/my-secret
    15	time=2024-09-29T11:52:19.723Z level=INFO msg=Updating key=default/my-secret
    16	time=2024-09-29T11:55:03.572Z level=INFO msg=Updating key=default/my-secret

Benefits
The controller takes longer to give up on a Sealed Secret.

Possible drawbacks
There will be more retries when the unseal error is legit, but that shouldn't cause any issues because of the exponential backoff.

Applicable issues

• fixes Secret deleted by the garbage collector with delay #1599

[agarcia-oss]

Hi @alemorcuq, I wonder if it'll be a better option to make the number of retries a configurable flag for the controller instead. WDYT?