Agent tags should not be allowed to be special characters

Issue originally raised in Fleet UI: https://github.com/elastic/kibana/issues/135775

The same issue can happen when tags are set with agent enroll command.

**Steps to reproduce:**
1. Enroll an agent with `--tag` option with special characters say, `"Tags"`
2. Navigate to Kibana Fleet>Agents tab.
3. Click on Tags dropdown filter and select `"Tags"`.
4. Observe error pop-ups related to `Kuery is malformed:`

**Expected Result:**
User should not be able to enroll agents with tags with unsupported special characters which could show errors on selecting from tags filter.

Start with the agent enroll command's --tag handling and reproduce the issue using a tag containing special characters such as "Tags". Trace where tags are accepted and verify that unsupported values are rejected during enrollment; done means selecting tags in Kibana Fleet no longer produces malformed Kuery errors.

Written by the indexing model from the issue text.