feat: add possibility to change the timeout for the curl's connect phase

[gladkia]

Hi @gaborcsardi,

Please find a small PR with suggestions on how to implement this improvement.

Details:

• the timeout is set to 60[s] by default
• the timeout can be changed via options(timeout = X_SECONDS)

Example scenario:

> options(timeout = 2)
> getOption("timeout")
[1] 2
> Sys.setenv(R_PKG_SEARCH_SERVER = "search.r-pkg.org:4321")
> pkgsearch::advanced_search(Author = "John", Author = "Doe")
Error in curl::curl_fetch_memory(url, handle = handle) : 
  Timeout was reached: [search.r-pkg.org:4321] Connection timed out after 2003 milliseconds
> Sys.getenv("R_PKG_SEARCH_SERVER")
[1] "search.r-pkg.org:4321"
> Sys.unsetenv("R_PKG_SEARCH_SERVER")
> pkgsearch::advanced_search(Author = "John", Author = "Doe")
- "advanced search" ---------------------------------------------------------------------- 0 packages in 0.024 seconds 

[gaborcsardi]

Thank you!