Add ignore_transactions to SDK

[smeubank]

As described in the SDK Develop specs we want to add some tools to our SDK to make life easier to for devs who want to cut out some noise from their Sentry feeds. Less crap more good stuff.

getsentry/develop#884

for ruby there is already something reasonably similar to ignore_errors

in ruby, ignore_errors is called excluded_exceptions (we can deprecate and rename if necessary, but I think it's fine).
ignore_transactions doesn't exist.

[getsantry]

Assigning to @getsentry/support for routing, due by Monday, April 17th at 5:00 pm (sfo). ⏲️

[github-actions]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀