feat(jinja): add b64decode/b64encode builtin filters #3861

Job	Run time
changes	5s
test-dbt-versions (1.9)	1m 41s
test-dbt-versions (1.6)	1m 32s
test-dbt-versions (1.8)	1m 40s
test-dbt-versions (1.10)	1m 25s
test-dbt-versions (1.3)	1m 42s
test-dbt-versions (1.4)	1m 31s
test-dbt-versions (1.5)	1m 38s
test-dbt-versions (1.7)	1m 42s
test-vscode	0s
test-vscode-e2e	-7s
doc-tests	39s
migration-test	1m 27s
cicd-tests-windows	11m 26s
style-and-cicd-tests (3.10)	15m 10s
style-and-cicd-tests (3.13)	19m 6s
style-and-cicd-tests (3.11)	22m 56s
style-and-cicd-tests (3.12)	24m 33s
style-and-cicd-tests (3.9)	23m 54s
engine-tests-docker (mssql)	1m 46s
engine-tests-docker (trino)	9m 6s
engine-tests-docker (duckdb)	1m 31s
engine-tests-docker (postgres)	2m 6s
engine-tests-docker (mysql)	1m 39s
engine-tests-docker (starrocks)	3m 17s
engine-tests-docker (risingwave)	2m 38s
engine-tests-docker (clickhouse)	2m 35s
engine-tests-docker (spark)	5m 3s
ui-test	-1s
ui-style	-1s
engine-tests-cloud	-1s
	2h 41m 38s

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