Add custom timeout for ACME DNS validation

[jwgn]

Is your feature request related to a problem? Please describe.
ACME DNS validation with deSEC failed multiple times. It seems the timeout is too tight.
In Proxmox, I faced the same problem, adding a 30 second additional timeout in the GUI solved it.

Describe the solution you'd like
Please add a customizable timeout option to the GUI.

Describe alternatives you've considered
None.

Additional context
This is related to discussion #268

[jwgn]

Error: one or more domains had a problem: [<domain>.de] acme: error: 400 :: urn:ietf:params:acme:error:dns :: DNS problem: NXDOMAIN looking up TXT for _acme-challenge.<domain>.de - check that a DNS record exists for this domain

Happens over and over again. TXT record is correctly created and deleted afterwards. Have to request the certificate a dozen times until it works. Please increase the timeout or make it customizable.

[tobychui]

Hey @jwgn,

What DNS service provider you are using? Have you tried HTTP challenge as a work around for now?
I have just graduated last month and I am in the progress of moving to another city for my first job. I probably don't have time to fix anything in recent time, so if you need it urgently, please create a PR with the feature you want and I will try my best to review it asap. Thanks!

[jwgn]

I am using deSEC, as stated in the initial message. HTTP challenge works.