Add option for auto creation of inst/CITATION

[dieghernan]

Description

New parameter r_citation in cff_write(). When it is set to TRUE a
R citation file (inst/CITATION) would be generated/updated with the
information of the generated CITATION.cff file. No backup copy would be
created

Related Issue

Close #79

Example

Use case:

cff_write(r_citation = TRUE)

What do you think @roaldarbol @njtierney?

[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
188	2	186	0

View the full list of 2 ❄️ flaky tests

deprecated cff_extract_to_bibtex

Flake rate in main: 37.50% (Passed 10 times, Failed 6 times)

Stack Traces | 0.026s run time

Error in `cff_create("cffr")`: `x` not valid. If it is a package you may need to install it with `install.packages()`.
Backtrace:
    x
 1. \-cffr::cff_create("cffr") at test-deprecated.R:2:3
 2.   \-cli::cli_abort(paste0("{.arg x} not valid. ", msg_hint)) at cffr/R/cff_create.R:131:5
 3.     \-rlang::abort(...)

deprecated cff_to_bibtex

Flake rate in main: 37.50% (Passed 10 times, Failed 6 times)

Stack Traces | 0.063s run time

Error in `cff_create("cffr")`: `x` not valid. If it is a package you may need to install it with `install.packages()`.
Backtrace:
    x
 1. \-cffr::cff_create("cffr") at test-deprecated.R:11:3
 2.   \-cli::cli_abort(paste0("{.arg x} not valid. ", msg_hint)) at cffr/R/cff_create.R:131:5
 3.     \-rlang::abort(...)

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[roaldarbol]

Looks good to me!