Update Snakemake files types to include `Snakefile` to provide syntax detection

[lparsons]

Adding to #50978, files names Snakefile should also have python syntax detection. Snakefile is the default name for Snakemake files:

Snakemake tries to execute the workflow specified in a file called Snakefile in the same directory (instead, the Snakefile can be given via the parameter -s).

[lparsons]

Thanks @aeschli !