Add `board_deparse` generic

[juliasilge]

This PR adds a board_deparse generic that will generate a character string of R code from a board object, like so:

library(pins)

b <- board_rsconnect()
#> Connecting to RSC 1.9.0.1 at <https://colorado.rstudio.com/rsc>
board_deparse(b)
#> board_rsconnect(server = "colorado.rstudio.com")

^{Created on 2021-09-24 by the reprex package (v2.0.1)}

This will be helpful for when we use a pin locally and need to write code to access the same pin from another machine.

This draft right only implements board_deparse for RStudio Connect and shows how we would use it in the RSC bundle. I put the generic in board.R since it applies to all boards but I could make a new deparse.R if you prefer.

Still TODO, after any changes needed here:

• Rest of boards
• Add tests

Anything else?

[juliasilge]

I have this working pretty nicely for S3, I think:

library(pins)

b <- board_s3("pins-test-julia", region = "us-east-2")
board_deparse(b)
#> board_s3(bucket = "pins-test-julia", region = "us-east-2")

^{Created on 2021-09-24 by the reprex package (v2.0.1)}

I don't have the env variables and such to be able to regenerate the snapshots for RSC and S3. Why is the CI all green if I added tests but didn't update the snapshots? (I did update snapshots for board_local() and board_url() which by the way just errors.)

Still TODO is Azure, for which I don't have an account so I'll be doing a bit of blindly stabbing in the dark.

Is it useful to have this for Kaggle?

[juliasilge]

Here are some open questions to answer/confirm/address:

• board_deparse() is not implemented for Kaggle for now (can come back to it if users would find it useful)
• The snapshots need to be regenerated (I don't have the right keys, etc)
• Should profile be included on AWS or not?

[hadley]

• For board_kaggle_*(), I think you can just assume that username/key will come from a kaggle.json so the method can be very simple
• Will regenerate momentarily. CI looks good because generating the first snapshot is only a warning, not a failure. I wonder if it should be an error on CI?
• I'll check with Joe, but think profile should not be included — I suspect a common use would be profile = "production" vs profile = "development"

[hadley]

@juliasilge can you take one last pass through this please? (I'm aiming for submission on Friday.

[juliasilge]

I installed from this branch again and ran through all the setups I have -- everything is working 👍

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