add `transactionIgnoreUserAgents` config var using wildcard-matcher, deprecate `ignoreUserAgents`

From discussion on https://github.com/elastic/apm/issues/395 it was noted that the "ignore_user_agents" config var in the Java agent is the only "dynamic" config var that (a) has the same name as a config var in another language agent, but (b) is not consistent in semantics. To get all dynamic config vars to also be *central config* vars, those vars need to be consistent across agents. The proposal from discussion is to:

1. for now mark `ignore_user_agents` in the Java agent as *not* dynamic (https://github.com/elastic/apm-agent-java/issues/1632)
2. plan to change the Node.js Agent's handling of `ignoreUserAgents` to be consistent (i.e. to use Wildcard Matcher patterns). That is this ticket. This will need to wait for the next major version as it is technically a backward incompatible change. I say "technically" because we don't have data or indication that there is any customer usage of this config var.

# proposed change to `ignoreUserAgents` semantics

Currently `ignoreUserAgents` takes an array of strings or regexps. If a string, it is "matched against the beginning of the User-Agent."

Proposed changes

- A string entry in the array is interpreted as a wildcard matcher pattern. This is a breaking change. Customers typically using an entry like `"foo"` would need to change it to `"foo*"` to get the same matching behaviour.
- A RegExp entry in the array is taken as is. This doesn't conflict with central config handling, because central config returns a comma-separated string -- i.e. it only supports passing wildcard matcher patterns.

An alternative proposal:

- Create a new config var, e.g. `ignoreUserAgents2` or `transactionIgnoreUserAgents` (I'm not married to the name) that takes the new semantics (compare to `transactionIgnoreUrls`) and is connected to the central `ignore_user_agents` config var.
- Deprecate or drop the old `ignoreUserAgents`.

**Edit**: The "alternative proposal" is the winner (see comments below).