Add dt to GenericBackendV2

[ElePT]

Summary

This PR allows to configure dt from the GenericBackendV2 init, a useful feature for some scheduling tests. This should have been added from the start but was likely left out as an oversight.

Details and comments

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core

[mtreinish]

LGTM, thanks for doing this

[coveralls]

Pull Request Test Coverage Report for Build 13287509449

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 12 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.002%) to 88.317%

---

Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/unitary_synthesis.rs	2	93.4%
crates/qasm2/src/lex.rs	4	91.98%
crates/qasm2/src/parse.rs	6	97.61%

Totals
Change from base Build 13271264264:	0.002%
Covered Lines:	78804
Relevant Lines:	89229

---

💛 - Coveralls