Add 'self' to CSP policy

[komuw]

• The previous policy was preventing media files from been served in localhost

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.03% :warning:

Comparison is base (cd0f168) 73.34% compared to head (0873a27) 73.32%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #379 +/- ## ========================================== - Coverage 73.34% 73.32% -0.03% ========================================== Files 47 47 Lines 5602 5604 +2 ========================================== Hits 4109 4109 - Misses 1201 1203 +2 Partials 292 292 ``` | [Files Changed](https://app.codecov.io/gh/komuw/ong/pull/379?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Komu+Wairagu) | Coverage Δ | | |---|---|---| | [middleware/security.go](https://app.codecov.io/gh/komuw/ong/pull/379?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Komu+Wairagu#diff-bWlkZGxld2FyZS9zZWN1cml0eS5nbw==) | `100.00% <100.00%> (ø)` | | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/komuw/ong/pull/379/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Komu+Wairagu)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.