Agnosticize integrations HTTP error handling (batch 2 of 3)

[mwdd146980]

What does this PR do?

Removes backend-specific requests references from the next set of integrations, leaving each on the HTTP-agnostic surface only. Per integration it narrows self.http catch sites to datadog_checks.base.utils.http_exceptions.* (no dual-catch), swaps bare from requests import ... to agnostic names, drops now-unused requests imports, and updates the interception-path tests (agnostic exceptions, MockHTTPResponse, and the mock_http/mock_openmetrics_http fixtures).

Integrations covered (batch 2 of 3): fly_io, gitlab, harbor, hdfs_datanode, hdfs_namenode, ibm_db2, kubelet, kyototycoon, mapreduce, marathon, marklogic, mesos_master.

The backend stays requests. Behavior is unchanged. This PR is based directly on #24516 for now. When #24516 is approved, it will be merged into #22676, and then this PR will be stacked on #22676.

Motivation

Checks and their tests should depend only on the agnostic HTTP surface (http_exceptions.*), never on requests-specific APIs, so the backend can later be swapped without touching consumers.

Verification

• Touched production packages are free of requests imports/attribute use.
• Catch sites reference only http_exceptions.*. No (RequestException, HTTPError) dual-catch remains.
• Per-integration unit tests were run and pass in the source work. ddev test --lint is green across the touched integrations.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add qa/required if this PR needs QA validation, or qa/skip-qa if it does not. Exactly one of the two is required.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[datadog-official]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.
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[NouemanKHAL]

LGTM for the code!
Blocker: changelog entries should either by a .added or omitted in this PR and only generated when merging to master as this is a dev change, we only want a changelog for the user-facing changes (when merging to master)

[dd-octo-sts]

Validation Report

All 21 validations passed.

Show details

Validation	Description	Status
agent-reqs	Verify check versions match the Agent requirements file	✅
ci	Validate CI configuration and code coverage settings	✅
codeowners	Validate every integration has a CODEOWNERS entry	✅
config	Validate default configuration files against spec.yaml	✅
dep	Verify dependency pins are consistent and Agent-compatible	✅
http	Validate integrations use the HTTP wrapper correctly	✅
imports	Validate check imports do not use deprecated modules	✅
integration-style	Validate check code style conventions	✅
jmx-metrics	Validate JMX metrics definition files and config	✅
labeler	Validate PR labeler config matches integration directories	✅
legacy-signature	Validate no integration uses the legacy Agent check signature	✅
license-headers	Validate Python files have proper license headers	✅
licenses	Validate third-party license attribution list	✅
metadata	Validate metadata.csv metric definitions	✅
models	Validate configuration data models match spec.yaml	✅
openmetrics	Validate OpenMetrics integrations disable the metric limit	✅
package	Validate Python package metadata and naming	✅
qa-label	Validate the pull request declares whether it needs QA for the next Agent release	✅
readmes	Validate README files have required sections	✅
saved-views	Validate saved view JSON file structure and fields	✅
version	Validate version consistency between package and changelog	✅

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