github: Add graphql utility class to contain query fields

[jerry-skydio]

This makes it easier to dynamically construct and resize queries, which
should improve retry behavior in a followup.

[jerry-skydio]

Reviews in this chain:
└#253 github: Add graphql utility class to contain query fields
　└#254 github: Add request retry splitting
　　└#255 test: Add github tests

[jerry-skydio]

#	head	base	diff	date	summary
0	978add51	4599c0ba	diff	May 20 17:00 PM	3 files changed, 892 insertions(+), 472 deletions(-)
1	550ecf7b	4599c0ba	diff	May 21 13:44 PM	1 file changed, 274 deletions(-)
2	3466dcba	b7cbff59	rebase	Jun 19 10:47 AM	0 files changed
3	252ff615	aab90897	diff	Jun 19 12:49 PM	0 files changed
4	9645b7ff	d1589ef0	diff	Jun 19 13:17 PM	1 file changed, 31 insertions(+), 23 deletions(-)
5	262cc29f	d1589ef0	diff	Jun 19 13:24 PM	1 file changed, 6 insertions(+), 6 deletions(-)
6	07520e54	d8008423	rebase	Jun 26 10:38 AM	0 files changed