Normalize namespace and metric names.

[walerian777]

What does this PR do?

According to the documentation metric names contain only ASCII alphanumerics, underscores, and periods, while other characters are converted to underscores.

Invalid names can lead to malformed dogstatsd packets being created.

It solves #740.

Description of the Change

This commit ensures we replace all invalid characters with underscores for both namespaces and metric names.

A similar thing has been already done for tags in #489 and #517, so I followed the example.

Possible Drawbacks

Performance cost due to string manipulation - partially addressed by using cache.

Verification Process

Tested manually. Added unit tests.

Release Notes

If some metrics with invalid names were successfully pushed, this might impose backward incompatibility.

Review checklist (to be filled by reviewers)

• [ ] Feature or bug fix MUST have appropriate tests (unit, integration, etc...)
• [ ] PR title must be written as a CHANGELOG entry (see why)
• [ ] Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• [ ] PR must have one changelog/ label attached. If applicable it should have the backward-incompatible label attached.
• [ ] PR should not have do-not-merge/ label attached.
• [ ] If Applicable, issue must have kind/ and severity/ labels attached at least.

[github-actions[bot]]

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