chore: sort headers alphabetically

[yenfryherrerafeliz]

Issue #3241

Description of changes:
Sorts presigned headers alphabetically.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[stobrien89]

Needs a changelog entry and integ/smoke test runs

[yenfryherrerafeliz]

vendor/bin/behat --format=progress --suite=smoke --tags='~@noassumerole'
...................................................................... 70
...................................................................... 140
...................................................................... 210
............

111 scenarios (111 passed)
222 steps (222 passed)
0m37.42s (93.51Mb)

vendor/bin/behat --format=progress --tags=integ
...................................................................... 70
...................................................................... 140
...................................................................... 210
...................................................................... 280
...................................................................... 350
...................................................................... 420
...............

127 scenarios (127 passed)
435 steps (435 passed)
21m55.09s (46.50Mb)