Enhancement: Support for Vector or List of Emails for Multiple Recipients

[nikitoshina]

This pull request introduces the ability to pass a vector or list of emails to the function, enabling the creation of an email with multiple recipients. This feature addresses an issue encountered by our team, where there was an assumption that the function could naturally handle a vector/list of emails for sending to multiple recipients. A thorough search revealed no documentation on how to achieve this, indicating a gap in usability for users unfamiliar with the underlying mechanics of the function.

The addition of this feature simplifies the process of including multiple recipients, CCs, and BCCs, making it more accessible and user-friendly, especially for those not versed in the function's inner workings.

[github-actions]

[air] _{reported by reviewdog 🐶}

Suggested change

	x$header$To <- paste(val, collapse=",")
	x$header$To <- paste(val, collapse = ",")

[github-actions]

[air] _{reported by reviewdog 🐶}

Suggested change

	x$header$Cc <- paste(val, collapse=",")
	x$header$Cc <- paste(val, collapse = ",")

[github-actions]

[air] _{reported by reviewdog 🐶}

Suggested change

	x$header$Bcc <- paste(val, collapse=",")
	return(x)
	x$header$Bcc <- paste(val, collapse = ",")
	return(x)

[jennybc]

Thanks and sorry this sat for so long! Once I reviewed it, I found tests suggesting that multiple recipients already works for To, Cc, and Bcc:

gmailr/tests/testthat/test-gm_mime.R

Lines 25 to 44 in 9630af7

	rv <- gm_to(msg, c("adam@ali.as", "another@ali.as", "bob@ali.as"))
	expect_equal(
	header_encode(rv$header$To),
	"adam@ali.as, another@ali.as, bob@ali.as",
	label = "to (multiple) sets To header"
	)
	rv <- gm_cc(msg, c("adam@ali.as", "another@ali.as", "bob@ali.as"))
	expect_equal(
	header_encode(rv$header$Cc),
	"adam@ali.as, another@ali.as, bob@ali.as",
	label = "cc (multiple) sets To header"
	)
	rv <- gm_bcc(msg, c("adam@ali.as", "another@ali.as", "bob@ali.as"))
	expect_equal(
	header_encode(rv$header$Bcc),
	"adam@ali.as, another@ali.as, bob@ali.as",
	label = "bcc (multiple) sets To header"
	)

And documentation also indicating that a vector can be provided to gm_to(val =) and friends:

gmailr/R/gm_mime.R

Line 45 in 9630af7

#' @param val the value to set, can be a vector, in which case the values will be joined by ", ".

I also manually tested the functionality and it already works. So I added an example to hopefully make this more discoverable, but we don't need to change the code as per this PR.