fix: prevent duplicating metrics middleware

[yenfryherrerafeliz]

Issue #3086

Description of changes:

• Prevent adding the same metrics middleware multiple times.

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

[yenfryherrerafeliz]

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

66 scenarios (66 passed)
248 steps (248 passed)
9m4.85s (42.06Mb)

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

112 scenarios (112 passed)
224 steps (224 passed)
0m36.32s (95.28Mb)

[stobrien89]

Just a doc nit and an extra assertion needed on the test. We need a changelog entry for this as well