:sparkles: WIP: Create a Go pkg with a managed content caching layer

[everettraven]

Description

• Adds a new internal package internal/contentmanager that has an implementation of a dynamic caching layer for managing watches on content managed by a ClusterExtension

Fixes #974

Reviewer Checklist

• [ ] API Go Documentation
• [ ] Tests: Unit Tests (and E2E Tests, if appropriate)
• [ ] Comprehensive Commit Messages
• [ ] Links to related GitHub Issue(s)

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 70.11494% with 26 lines in your changes missing coverage. Please review.

Project coverage is 77.48%. Comparing base (00eb488) to head (aacf231). Report is 8 commits behind head on main.

Files	Patch %	Lines
internal/contentmanager/contentmanager.go	70.11%	18 Missing and 8 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1001 +/- ## ========================================== + Coverage 77.19% 77.48% +0.28% ========================================== Files 17 19 +2 Lines 1206 1337 +131 ========================================== + Hits 931 1036 +105 - Misses 193 211 +18 - Partials 82 90 +8 ``` | [Flag](https://app.codecov.io/gh/operator-framework/operator-controller/pull/1001/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=operator-framework) | Coverage Δ | | |---|---|---| | [e2e](https://app.codecov.io/gh/operator-framework/operator-controller/pull/1001/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=operator-framework) | `56.54% <ø> (ø)` | | | [unit](https://app.codecov.io/gh/operator-framework/operator-controller/pull/1001/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=operator-framework) | `54.67% <70.11%> (+2.76%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=operator-framework#carryforward-flags-in-the-pull-request-comment) to find out more.

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