add escaping for backslashes, fixes #718

[oliverrahner]

Closes #718

Proposed Changes

Backslashes should also be escaped. This is generally optional in InfluxDB, but in special cases such as the end of a tag value, it might become crucial

Checklist

• [x] CHANGELOG.md updated
• [x] Rebased/mergeable
• [x] A test has been added if appropriate
• [x] mvn test completes successfully
• [x] Commit messages are conventional
• [x] Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.39%. Comparing base (dc1d442) to head (8f23758).

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #720 +/- ## ============================================ + Coverage 88.37% 88.39% +0.01% + Complexity 786 784 -2 ============================================ Files 174 174 Lines 7091 7093 +2 Branches 391 391 ============================================ + Hits 6267 6270 +3 + Misses 698 697 -1 Partials 126 126 ```

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[oliverrahner]

Good thing you asked about the integration tests... turns out my fix doesn't work :-/ I'll work on it.

[oliverrahner]

So, this probably still is true: https://github.com/influxdata/docs.influxdata.com-ARCHIVE/issues/2676 I've opened a new docs issue here: https://github.com/influxdata/docs-v2/issues/5481

Not fully aware of this library's policy, should it try to inform the user about the actual cause of the issue, such as a tag value ending in a backslash? Or should this be left to the Influx daemon (which doesn't do a good job explaining the issue in this case)?

Independent from this question, the actual change introduced with this PR is probably still a good idea.