Allow specifying functions server port for netlify dev via flag

[jiri-matejka]

Is your feature request related to a problem? Please describe.
Every time I start netlify dev, functions run on different port. It makes it hard to create a collection of test requests in tools like Postman, because every time I need to change port number.

Describe the solution you'd like
I propose new parameter --functionsPort that would make possible to specify which port functions server runs on.

Describe alternatives you've considered
None

Can you submit a pull request?
No

[tinfoil-knight]

@jiri-matejka I think you can configure netlify.toml as follows to get a fixed port:

[dev]
	functionsPort = 8070

Does this work or are you specifically looking for a way to provide the flag through command line?

[jiri-matejka]

@tinfoil-knight It works perfectly and is totally acceptable to store it in the file. Closing the issue then.

EDIT: It seems it's not documented (looking at https://docs.netlify.com/configure-builds/file-based-configuration/#netlify-dev), it would be worth documenting, IMO.

[erezrokah]

Re-opening as I think it's good to have as a flag as well + document it

[tinfoil-knight]

@erezrokah Can I take up the issue?